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Microsoft Exchange 2016 Edge Transport Server Security Technical Implementation Guide

Version 2 Release 21
2021-01-222020-10-23
U_MS_Exchange_2016_Edge_Transport_Server_STIG_V2R21_Manual-xccdf.xml
This Security Technical Implementation Guide is published as a tool to improve the security of Department of Defense (DoD) information systems. The requirements are derived from the National Institute of Standards and Technology (NIST) 800-53 and related documents. Comments or proposed revisions to this document should be sent via email to the following address: disa.stig_spt@mail.mil.

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Vulnerabilities (69)

Exchange must limit the Receive connector timeout.

Finding ID
EX16-ED-000010
Rule ID
SV-221202r612603_rule221202r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000001
CCI
CCI-000054
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practices strategies for setting tuning. This configuration controls the number of idle minutes before the connection is dropped. It works in conjunction with the Maximum Inbound Connections Count setting. Connections, once established, may incur delays in message transfer. If the timeout period is too long, there is risk that connections may be maintained for unnecessarily long time periods, preventing new connections from being established.

Fix Text

Update the EDSP, or the applicable documentation. Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -ConnectionTimeout 00:05:00 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedures for each Receive connector.

Check Content

Review the Email Domain Security Plan (EDSP), or Organizations applicable documentation. Determine the connection Timeout value. Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, ConnectionTimeout For each Receive connector, if the value of "ConnectionTimeout" is not set to "00:05:00", this is a finding. or If "ConnectionTimeout" is set to another value other than "00:05:00" and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange servers must use approved DoD certificates.

Finding ID
EX16-ED-000020
Rule ID
SV-221203r612603_rule221203r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000033
CCI
CCI-000213
Target Key
(None)
Documentable
No
Discussion

To mitigate the risk of unauthorized access to sensitive information by entities that have been issued certificates by DoD-approved PKIs, all DoD systems (e.g., networks, web servers, and web portals) must be properly configured to incorporate access control methods that do not rely solely on the possession of a certificate for access. Successful authentication must not automatically give an entity access to an asset or security boundary. Authorization procedures and controls must be implemented to ensure each authenticated entity also has a validated and current authorization. Authorization is the process of determining whether an entity, once authenticated, is permitted to access a specific asset. Information systems use access control policies and enforcement mechanisms to implement this requirement. Access control policies include identity-based policies, role-based policies, and attribute-based policies. Access enforcement mechanisms include access control lists, access control matrices, and cryptography. These policies and mechanisms must be employed by the application to control access between users (or processes acting on behalf of users) and objects (e.g., devices, files, records, processes, programs, and domains) in the information system. This requirement is applicable to access control enforcement applications (e.g., authentication servers) and other applications that perform information and system access control functions.

Fix Text

Remove the non-DoD certificate and import the correct DoD certificates.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ExchangeCertificate | Select CertificateDomains, issuer If the value of "CertificateDomains" does not indicate it is issued by the DoD, this is a finding.

Exchange must have accepted domains configured.

Finding ID
EX16-ED-000030
Rule ID
SV-221204r612603_rule221204r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000038
CCI
CCI-001368
Target Key
(None)
Documentable
No
Discussion

Exchange may be configured to accept email for multiple domain names. This setting identifies the domains for which the server will accept mail. This check verifies the email server is not accepting email for unauthorized domains.

Fix Text

Update the EDSP. Open the Exchange Management Shell and enter the following command: Set-AcceptedDomain -Identity <'IdentityName'> -MakeDefault $true Note: The <IdentityName> value must be in single quotes.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the Accepted Domain values. Open the Exchange Management Shell and enter the following command: Get-AcceptedDomain | Select Name, DomainName, Identity, Default If the value of "Default" is not set to "True", this is a finding. or If the "Default" value for "AcceptedDomains" is set to another value other than "True" and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange must have auto-forwarding of email to remote domains disabled or restricted.

Finding ID
EX16-ED-000040
Rule ID
SV-221205r612603_rule221205r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000038
CCI
CCI-001368
Target Key
(None)
Documentable
No
Discussion

Attackers can use automated messages to determine whether a user account is active, in the office, traveling, and so on. An attacker might use this information to conduct future attacks. Ensure Automatic Forwards to remote domains are disabled, except for enterprise email that must be restricted to forward-only to .mil and .gov. domains. Before enabling this setting, first configure a remote domain.

Fix Text

For Non-Enterprise Mail Fix Text: Open the Exchange Management Shell and enter the following command: Set-RemoteDomain -Identity <'IdentityName'> -AutoForwardEnabled $false Note: The <IdentityName> value must be in single quotes. For Enterprise Mail Fix Text, enter the following commands: New-RemoteDomain -Name <NewDomainName> -DomainName <SMTP address space> Note: NewDomainName must be either a ".mil" or ".gov" domain. Set-RemoteDomain -Identity <'IdentityName'> -AutoForwardEnabled $true

Check Content

Non-Enterprise Mail Check Content: Open the Exchange Management Shell and enter the following command: Get-RemoteDomain | Select Name, DomainName, Identity, AutoForwardEnabled If the value of "AutoForwardEnabled" is not set to "False", this is a finding. Enterprise Mail Check Content: Open the Exchange Management Shell and enter the following command: Get-RemoteDomain | Select Name, DomainName, Identity, AutoForwardEnabled If the value of “AutoForwardEnabled” is “True” and “DomainName” is not set to a “.mil” and/or “.gov” domain(s), this is a finding.

Exchange external Receive connectors must be domain secure-enabled.

Finding ID
EX16-ED-000050
Rule ID
SV-221206r612603_rule221206r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000038
CCI
CCI-001368
Target Key
(None)
Documentable
No
Discussion

The Simple Mail Transfer Protocol (SMTP) connector is used by Exchange to send and receive messages from server to server. Several controls work together to provide security between internal servers. This setting controls the authentication method used for communications between servers. With this feature enabled, messages can be securely passed from a partner domain securely. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from server to server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption can be compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between servers.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -DomainSecureEnabled $true Note: The <IdentityName> value must be in single quotes. Repeat the procedures for each receive connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, DomainSecureEnabled For each receive connector, if the value of "DomainSecureEnabled" is not set to "True", this is a finding.

The Exchange email Diagnostic log level must be set to the lowest level.

Finding ID
EX16-ED-000060
Rule ID
SV-221207r612603_rule221207r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000089
CCI
CCI-000169
Target Key
(None)
Documentable
No
Discussion

Log files help establish a history of activities and can be useful in detecting attack attempts or determining tuning adjustments to improve availability. Diagnostic logging, however, characteristically produces large volumes of data and requires care in managing the logs to prevent risk of disk capacity denial of service conditions. Exchange diagnostic logging is broken up into 29 main "services", each of which has anywhere from 2 to 26 "categories" of events to be monitored. Moreover, each category may be set to one of four levels of logging: Lowest, Low, CAT II, and High, depending on how much detail one desires. The higher the level of detail, the more disk space required to store the audit material. Diagnostic logging is intended to help administrators debug problems with their systems, not as a general-purpose auditing tool. Because the diagnostic logs collect a great deal of information, the log files may grow large very quickly. Diagnostic log levels may be raised for limited periods of time when attempting to debug relevant pieces of Exchange functionality. Once debugging has finished, diagnostic log levels should be reduced again.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-EventLogLevel -Identity <'IdentityName\EventlogName'> -Level Lowest Note: The <IdentityName\EventlogName> value must be in single quotes.

Check Content

Open the Exchange Management Shell and enter the following command: Get-EventLogLevel If any "EventLogLevel" values returned are not set to "Lowest", this is a finding.

Exchange Connectivity logging must be enabled.

Finding ID
EX16-ED-000070
Rule ID
SV-221208r612603_rule221208r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000089
CCI
CCI-000169
Target Key
(None)
Documentable
No
Discussion

A connectivity log is a record of the SMTP connection activity of the outbound message delivery queues to the destination mailbox server, smart host, or domain. Connectivity logging is available on Hub Transport servers and Edge Transport servers. By default, connectivity logging is disabled. If events are not recorded, it may be difficult or impossible to determine the root cause of system problems or the unauthorized activities of malicious users. Note: Transport configuration settings apply to the organization/global level of the Exchange SMTP path. By checking and setting them at the Hub server, the setting will apply to both Hub and Edge roles.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-TransportService -Identity <'IdentityName'> -ConnectivityLogEnabled $true Note: The <IdentityName> value must be in single quotes.

Check Content

Open the Exchange Management Shell and enter the following command: Get-TransportService | Select Name, Identity, ConnectivityLogEnabled If the value of "ConnectivityLogEnabled" is not set to "True", this is a finding.

Exchange Queue monitoring must be configured with threshold and action.

Finding ID
EX16-ED-000080
Rule ID
SV-221209r612603_rule221209r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000111
CCI
CCI-000154
Target Key
(None)
Documentable
No
Discussion

Monitors are automated "process watchers" that respond to performance changes and can be useful in detecting outages and alerting administrators where attention is needed. Exchange has built-in monitors that enable the administrator to generate alerts if thresholds are reached, better enabling them to react in a timely fashion. This field offers choices of alerts when a "warning" or "critical" threshold is reached on the SMTP queue. A good rule of thumb (default) is to issue warnings when SMTP queue growth exceeds 10 minutes and critical messages when it exceeds 20 minutes, which should only exist occasionally. Frequent alerts against this counter may indicate a network or other issue (such as inbound SPAMMER traffic) that directly impacts email delivery. Notification choices include email alert to an email-enabled account (e.g., an email Administrator) or invoke a script to take other action (e.g., to add an Event to the Microsoft Application Event Log, where external monitors might detect it).

Fix Text

Open the Exchange Management Shell and enter the following command: perfmon In the left pane, navigate to Performance >> Data Collector Sets >> User Defined. In left pane, right-click on User Defined >> New >> Data Collector Set and configure the system to use the data collection set for monitoring the queues.

Check Content

Note: If a third-party application is performing monitoring functions, the reviewer should verify the application is monitoring correctly and mark the vulnerability NA. Open the Exchange Management Shell and enter the following command: perfmon In the left pane, navigate to Performance >> Data Collector Sets >> User Defined. If no sets are defined or queues are not being monitored, this is a finding.

Exchange must not send Customer Experience reports to Microsoft.

Finding ID
EX16-ED-000090
Rule ID
SV-221210r612603_rule221210r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000141
CCI
CCI-000381
Target Key
(None)
Documentable
No
Discussion

It is detrimental for applications to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities or services are often overlooked and therefore may remain unsecured. They increase the risk to the platform by providing additional attack vectors. Applications are capable of providing a wide variety of functions and services. Some of the functions and services, provided by default, may not be necessary to support essential organizational operations (e.g., key missions, functions). Examples of non-essential capabilities include, but are not limited to, advertising software or browser plug-ins not related to requirements or providing a wide array of functionality not required for every mission, but cannot be disabled. All system errors in Exchange will result in outbound traffic that may be identified by an eavesdropper. For this reason, the "Report Fatal Errors to Microsoft" feature must be disabled.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-OrganizationConfig -CustomerFeedbackEnabled $false

Check Content

Open the Exchange Management Shell and enter the following command: Get-OrganizationConfig | Select Name, Identity, CustomerFeedbackEnabled If the value for "CustomerFeedbackEnabled" is not set to "False", this is a finding.

Exchange Audit data must be protected against unauthorized access (read access).

Finding ID
EX16-ED-000100
Rule ID
SV-221211r612603_rule221211r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000118
CCI
CCI-000162
Target Key
(None)
Documentable
No
Discussion

Log files help establish a history of activities and can be useful in detecting attack attempts or determining tuning adjustments to improve availability. Audit log content must always be considered sensitive and in need of protection. Audit data available for modification by a malicious user can be altered to conceal malicious activity. Audit data might also provide a means for the malicious user to plan unauthorized activities that exploit weaknesses. The contents of audit logs are protected against unauthorized access, modification, or deletion. Only authorized auditors and the audit functions should be granted read and write access to audit log data.

Fix Text

Update the EDSP to reflect the authorized groups or users that should have read access to the audit data. Restrict any unauthorized groups' or users' read access to the audit logs.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the authorized groups or users that should have read access to the audit data. If any group or user has read access to the audit data that is not documented in the EDSP, this is a finding.

Exchange Send Fatal Errors to Microsoft must be disabled.

Finding ID
EX16-ED-000110
Rule ID
SV-221212r612603_rule221212r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000141
CCI
CCI-000381
Target Key
(None)
Documentable
No
Discussion

It is detrimental for applications to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities or services are often overlooked and therefore may remain unsecured. They increase the risk to the platform by providing additional attack vectors. Applications are capable of providing a wide variety of functions and services. Some of the functions and services, provided by default, may not be necessary to support essential organizational operations (e.g., key missions, functions). Examples of non-essential capabilities include, but are not limited to, advertising software or browser plug-ins not related to requirements or providing a wide array of functionality not required for every mission, but cannot be disabled. Customer Experience reports in Exchange will result in outbound traffic that may be identified by an eavesdropper. For this reason, the Customer Experience reports to Microsoft must not be sent.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ExchangeServer -Identity <'IdentityName'> -ErrorReportingEnabled $false Note: The <IdentityName> value must be in single quotes. Repeat the procedure for each Identity.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ExchangeServer –status | Select Name, Identity, ErrorReportingEnabled For each exchange server, if the value of "ErrorReportingEnabled" is not set to "False", this is a finding.

Exchange audit data must be protected against unauthorized access for modification.

Finding ID
EX16-ED-000120
Rule ID
SV-221213r612603_rule221213r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000119
CCI
CCI-000163
Target Key
(None)
Documentable
No
Discussion

Log files help establish a history of activities and can be useful in detecting attack attempts or determining tuning adjustments to improve availability. Audit log content must always be considered sensitive and in need of protection. Audit data available for modification by a malicious user can be altered to conceal malicious activity. Audit data might also provide a means for the malicious user to plan unauthorized activities that exploit weaknesses. The contents of audit logs are protected against unauthorized access, modification, or deletion. Only authorized auditors and the audit functions should be granted read and write access to audit log data.

Fix Text

Update the EDSP to reflect the authorized groups or users that should have modify permissions to the audit data. Restrict any unauthorized groups' or users' modify permissions for the audit logs.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the authorized groups or users that should have modify permissions to the audit data. If any group or user has modify permissions for the audit data that is not documented in the EDSP, this is a finding.

Exchange audit data must be protected against unauthorized access for deletion.

Finding ID
EX16-ED-000130
Rule ID
SV-221214r612603_rule221214r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000120
CCI
CCI-000164
Target Key
(None)
Documentable
No
Discussion

Log files help establish a history of activities and can be useful in detecting attack attempts or determining tuning adjustments to improve availability. Audit log content must always be considered sensitive and in need of protection. Audit data available for modification by a malicious user can be altered to conceal malicious activity. Audit data might also provide a means for the malicious user to plan unauthorized activities that exploit weaknesses. The contents of audit logs are protected against unauthorized access, modification, or deletion. Only authorized auditors and the audit functions should be granted read and write access to audit log data.

Fix Text

Update the EDSP to reflect the authorized groups or users that should have delete permissions for the audit data. Restrict any unauthorized groups' or users' delete permissions for the audit logs.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the authorized groups or users that should have delete permissions for the audit data. If any group or user has delete permissions for the audit data that is not documented in the EDSP, this is a finding.

Exchange audit data must be on separate partitions.

Finding ID
EX16-ED-000140
Rule ID
SV-221215r612603_rule221215r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000125
CCI
CCI-001348
Target Key
(None)
Documentable
No
Discussion

Log files help establish a history of activities and can be useful in detecting attack attempts or determining tuning adjustments to improve availability. Audit log content must always be considered sensitive and in need of protection. Successful exploit of an application server vulnerability may well be logged by monitoring or audit processes when it occurs. Writing log and audit data to a separate partition where separate security contexts protect them may offer the ability to protect this information from being modified or removed by the exploit mechanism.

Fix Text

Update the EDSP. Configure the audit log location to be on a partition drive separate from the application.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the audit logs' assigned partition. Note: By default, the logs are located on the application partition in \Program Files\Microsoft\Exchange Server\V15\Logging\. If the log files are not on a separate partition from the application, this is a finding.

The Exchange local machine policy must require signed scripts.

Finding ID
EX16-ED-000150
Rule ID
SV-221216r612603_rule221216r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000131
CCI
CCI-001749
Target Key
(None)
Documentable
No
Discussion

Scripts, especially those downloaded from untrusted locations, often provide a way for attackers to infiltrate a system. By setting machine policy to prevent unauthorized script executions, unanticipated system impacts can be avoided.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ExecutionPolicy RemoteSigned

Check Content

Open the Exchange Management Shell and enter the following command: Get-ExecutionPolicy If the value returned is not "RemoteSigned", this is a finding.

Exchange Internet-facing Send connectors must specify a Smart Host.

Finding ID
EX16-ED-000160
Rule ID
SV-221217r612603_rule221217r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000213
CCI
CCI-001178
Target Key
(None)
Documentable
No
Discussion

When identifying a "Smart Host" for the email environment, a logical Send connector is the preferred method. A Smart Host acts as an Internet-facing concentrator for other email servers. Appropriate hardening can be applied to the Smart Host, rather than at multiple locations throughout the enterprise. Failure to identify a Smart Host could default to each email server performing its own lookups (potentially through protective firewalls). Exchange servers should not be Internet facing and should therefore not perform any Smart Host functions. When the Exchange servers are Internet facing, they must be configured to identify the Internet-facing server that is performing the Smart Host function.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SendConnector <'IdentityName'> -SmartHosts <'IP Address of Smart Host'> -DNSRoutingEnabled $false Note: The <IdentityName> value must be in single quotes. Repeat the procedures for each send connector.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the Internet-facing connectors. Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, SmartHosts, DNSRoutingEnabled For each send connector, if the value of "SmartHosts" does not return the Smart Host IP Address and the value for "DNSRoutingEnabled" is not set to "False", this is a finding.

Exchange internal Send connectors must use domain security (mutual authentication Transport Layer Security).

Finding ID
EX16-ED-000170
Rule ID
SV-221218r612603_rule221218r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000219
CCI
CCI-001184
Target Key
(None)
Documentable
No
Discussion

The Simple Mail Transfer Protocol (SMTP) connector is used by Exchange to send and receive messages from server to server. Several controls work together to provide security between internal servers. This setting controls the authentication method used for communications between servers. With this feature enabled, only servers capable of supporting domain authentication will be able to send and receive mail within the domain. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from server to server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption can be compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between servers.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SendConnector <'IdentityName'> -DomainSecureEnabled $true Note: The <IdentityName> value must be in single quotes. Repeat the procedures for each send connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, DomainSecureEnabled For each send connector, if the value of "DomainSecureEnabled" is not set to "True", this is a finding. If the "TlsAuthLevel" parameter is set to "DomainValidation" then the "TlsDomain" parameter is required if "DNSRoutingEnabled" parameter is set to "$false". The "DNSRoutingEnabled" parameter must be "$true" If the value of "DomainSecureEnabled" is "$true".

Exchange Internet-facing Receive connectors must offer Transport Layer Security (TLS) before using basic authentication.

Finding ID
EX16-ED-000180
Rule ID
SV-221219r612603_rule221219r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000219
CCI
CCI-001184
Target Key
(None)
Documentable
No
Discussion

Sending unencrypted email over the Internet increases the risk that messages can be intercepted or altered. TLS is designed to protect confidentiality and data integrity by encrypting email messages between servers and thereby reducing the risk of eavesdropping, interception, and alteration. This setting forces Exchange to offer TLS before using basic authentication.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -AuthMechanism 'Tls, BasicAuth, BasicAuthRequireTLS' Note: The <IdentityName> value must be in single quotes. Example only for the Identity: <ServerName>\Frontend <ServerName> Repeat the procedure for each receive connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, AuthMechanism For each receive connector, if the value of "AuthMechanism" is not set to "Tls, BasicAuth, BasicAuthRequireTLS", this is a finding.

Exchange Outbound Connection Timeout must be 10 minutes or less.

Finding ID
EX16-ED-000190
Rule ID
SV-221220r612603_rule221220r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. This configuration controls the number of idle minutes before the connection is dropped. It works in conjunction with the Maximum Outbound Connections Count setting. Connections, once established, may incur delays in message transfer. The default of 10 minutes is a reasonable window in which to resume activities without maintaining idle connections for excessive intervals. If the timeout period is too long, idle connections may be maintained for unnecessarily long time periods, preventing new connections from being established. Sluggish connectivity increases the risk of lost data. A value of 10 or less is optimal.

Fix Text

Update the EDSP to reflect the Connection Timeout value. Open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'IdentityName'> -ConnectionInactivityTimeOut 00:10:00 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedure for each send connector.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the Connection Timeout value. Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, ConnectionInactivityTimeOut For each send connector, if the value of "ConnectionInactivityTimeOut" is not set to "00:10:00", this is a finding. or If "ConnectionInactivityTimeOut" is set to other than "00:10:00" and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange Outbound Connection Limit per Domain Count must be controlled.

Finding ID
EX16-ED-000200
Rule ID
SV-221221r612603_rule221221r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. This configuration controls the maximum number of simultaneous outbound connections from a domain and works in conjunction with the Maximum Outbound Connections Count setting as a delivery tuning mechanism. If the limit is too low, connections may be dropped. If the limit is too high, some domains may use a disproportionate resource share, denying access to other domains. Appropriate tuning reduces the risk of data delay or loss. By default, a limit of 20 simultaneous outbound connections from a domain should be sufficient. The value may be adjusted if justified by local site conditions.

Fix Text

Update the EDSP to reflect the value for Maximum Domain Connections. Open the Exchange Management Shell and enter the following command: Set-TransportService -Identity <'IdentityName'> -MaxPerDomainOutboundConnections 20 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the value for Maximum Domain Connections. Open the Exchange Management Shell and enter the following command: Get-TransportService | Select Name, Identity, MaxPerDomainOutboundConnections If the value of "MaxPerDomainOutboundConnections" is not set to "20", this is a finding. or If the value of "MaxPerDomainOutboundConnections" is set to a value other than "20" and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange Send connector connections count must be limited.

Finding ID
EX16-ED-000230
Rule ID
SV-221222r612603_rule221222r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

This setting controls the maximum number of simultaneous outbound connections allowed for a given SMTP Connector and can be used to throttle the SMTP service if resource constraints warrant it. If the limit is too low, connections may be dropped. If the limit is too high, some domains may use a disproportionate resource share, denying access to other domains. Appropriate tuning reduces the risk of data delay or loss.

Fix Text

Update the EDSP to reflect the value for SMTP Server Maximum Outbound Connections. Open the Exchange Management Shell and enter the following command: Set-TransportService -Identity <'IdentityName'> -MaxOutboundConnections 1000 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the value for SMTP Server Maximum Outbound Connections. Open the Exchange Management Shell and enter the following command: Get-TransportService | Select Name, Identity, MaxOutboundConnections If the value of "MaxOutboundConnections" is not set to "1000", this is a finding. or If the value of "MaxOutboundConnections" is set to a value other than "1000" and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange message size restrictions must be controlled on Send connectors.

Finding ID
EX16-ED-000240
Rule ID
SV-221223r612603_rule221223r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. For message size restrictions, multiple places exist to set or override inbound or outbound message size. Failure to control the configuration strategy can result in loss of data or system availability. This setting enables the administrator to control the maximum message size on a Send connector. Using connectors to control size limits may necessitate applying message size limitations in multiple places, with the potential of introducing conflicts and impediments in the mail flow. Changing this setting at the connector overrides the global one. Therefore, if operational needs require it, the connector value may be set lower than the global value with the rationale documented in the EDSP.

Fix Text

Update the EDSP to reflect the maximum message send size. Open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'IdentityName'> -MaxMessageSize <MaxSendSize> Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedure for each send connector.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the maximum message send size. Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, MaxMessageSize For each send connector, if the value of "MaxMessageSize" is not the same as the global value, this is a finding. or If "MaxMessageSize" is set to a numeric value different from the maximum message send size value documented in the EDSP, this is a finding.

Exchange Send connectors delivery retries must be controlled.

Finding ID
EX16-ED-000250
Rule ID
SV-221224r612603_rule221224r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

This setting controls the rate at which delivery attempts from the home domain are retried and user notifications are issued and notes the expiration time when the message will be discarded. If delivery retry attempts are too frequent, servers will generate network congestion. If they are too far apart, messages may remain queued longer than necessary, potentially raising disk resource requirements. The default values of these fields should be adequate for most environments. Administrators may wish to modify the values, but changes should be documented in the System Security Plan. Note: Transport configuration settings apply to the organization/global level of the Exchange SMTP path. By checking and setting them at the Hub server, the setting will apply to both Hub and Edge roles.

Fix Text

Update the EDSP to reflect the value for Transient Failure Retry Count. Open the Exchange Management Shell and enter the following command: Set-TransportService -Identity <'IdentityName'> -TransientFailureRetryCount 10 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the value for Transient Failure Retry Count. Open the Exchange Management Shell and enter the following command: Get-TransportService | Select Name, Identity, TransientFailureRetryCount If the value of "TransientFailureRetryCount" is not set to "10" or less, this is a finding. or If the value of "TransientFailureRetryCount" is set to more than "10" or has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange Send connectors must be clearly named.

Finding ID
EX16-ED-000260
Rule ID
SV-221225r612603_rule221225r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

For Send connectors, unclear naming as to direction and purpose increases risk that messages may not flow as intended, troubleshooting efforts may be impaired, or incorrect assumptions may be made about the completeness of the configuration. Collectively, connectors should account for all connections required for the overall email topology design. Simple Mail Transfer Protocol (SMTP) connectors, when listed, must name purpose and direction clearly, and their counterparts on servers to which they connect should be recognizable as their partners.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SendConnector -Name <'NewName'> -Identity <'IdentityName'> Note: Both the <NewName> and <IdentityName> values must be in single quotes. Repeat the procedure for each send connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity Review the naming for connectors. For each send connector, if the connectors are not clearly named for purpose and direction, this is a finding.

Exchange Receive connector Maximum Hop Count must be 60.

Finding ID
EX16-ED-000270
Rule ID
SV-221226r612603_rule221226r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. This setting controls the maximum number of hops (email servers traversed) a message may take as it travels to its destination. Part of the original Internet protocol implementation, the hop count limit prevents a message from being passed in a routing loop indefinitely. Messages exceeding the maximum hop count are discarded undelivered. Recent studies indicate that virtually all messages can be delivered in fewer than 60 hops. If the hop count is set too low, messages may expire before they reach their destinations. If set too high, an undeliverable message may cycle between servers, raising the risk of network congestion.

Fix Text

Update the EDSP to reflect the value for Receive connectors. Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -MaxHopCount 60 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedure for each receive connector.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the value for Receive connectors. Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, MaxHopCount For each receive connector, if the value of "MaxHopCount" is not set to "60", this is a finding. or If the value of "MaxHopCount" is set to a value other than "60" and has signoff and risk acceptance, this is not a finding.

Exchange Receive connectors must be clearly named.

Finding ID
EX16-ED-000280
Rule ID
SV-221227r612603_rule221227r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

For receive connectors, unclear naming as to direction and purpose increases risk that messages may not flow as intended, troubleshooting efforts may be impaired, or incorrect assumptions may be made about the completeness of the configuration. Collectively, connectors should account for all connections required for the overall email topology design. Simple Mail Transfer Protocol (SMTP) connectors, when listed, must name purpose and direction clearly, and their counterparts on servers to which they connect should be recognizable as their partners.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Name <'NewName'> -Identity <'IdentityName'> Note: Both the <NewName> and <IdentityName> value must be in single quotes. Repeat the procedure for each receive connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity For each Receive connector, review the naming for connectors. If the connectors are not clearly named for purpose and direction, this is a finding.

Exchange Receive connectors must control the number of recipients chunked on a single message.

Finding ID
EX16-ED-000290
Rule ID
SV-221228r612603_rule221228r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. For message size restrictions, multiple places exist to set or override inbound or outbound message size. Failure to control the configuration strategy can result in loss of data or system availability. This setting enables the administrator to enable "chunking" on received messages as they arrive at the domain. This is done so large message bodies can be relayed by the remote sender to the Receive connector in multiple, smaller chunks.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -ChunkingEnabled $true Note: The <IdentityName> value must be in single quotes. Repeat the procedure for each receive connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, ChunkingEnabled For each receive connector, if the value of "ChunkingEnabled" is not set to "True", this is a finding.

Exchange Receive connectors must control the number of recipients per message.

Finding ID
EX16-ED-000300
Rule ID
SV-221229r612603_rule221229r561307_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. This configuration controls the maximum number of recipients who will receive a copy of a message at one time. This tunable value is related to throughput capacity and can enable the ability to optimize message delivery. Note: There are two types of default Receive connecters: "Client Servername" accepts SMTP connections from all non-MAPI clients, such as POP and IMAP. As POP and IMAP are not authorized for use in DoD, these should not be present. Their default value for MaxRecipientsPerMessage is 200. IMAP Secure is not restricted and may be configured. "Default Servername" accepts connections from other mailbox servers and any Edge Transport servers. Their default value for MaxRecipientsPerMessage is 5000.

Fix Text

Update the EDSP to reflect the Maximum Recipients per Message value. Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -MaxRecipientsPerMessage 5000 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedure for each receive connector.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the Maximum Recipients per Message value. Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, MaxRecipientsPerMessage For each receive connector, if the value of "MaxRecipientsPerMessage" is not set to "5000", this is a finding. or If the value of "MaxRecipientsPerMessage" is set to a value other than "5000" and has signoff and risk acceptance in the EDSP, this is not a finding.

The Exchange Internet Receive connector connections count must be set to default.

Finding ID
EX16-ED-000310
Rule ID
SV-221230r612603_rule221230r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. This configuration controls the maximum number of simultaneous inbound connections allowed to the SMTP server. By default, the number of simultaneous inbound connections is 5000. If a limit is set too low, the connections pool may be filled. If attackers perceive the limit is too low, they could deny service to the Simple Mail Transfer Protocol (SMTP) server by using a connection count that exceeds the limit set. By setting the default configuration to 5000, attackers would need many more connections to cause denial of service.

Fix Text

Update the EDSP to reflect the Maximum Inbound connections value. Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -MaxInboundConnection 5000 Note: The <IdentityName> value must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedure for each receive connector.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the Maximum Inbound connections value. Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, MaxInboundConnection Identify Internet-facing connectors. For each receive connector, if the value of "MaxInboundConnection" is not set to "5000", this is a finding. or If "MaxInboundConnection" is set to a value other than "5000" or is set to unlimited and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange Message size restrictions must be controlled on Receive connectors.

Finding ID
EX16-ED-000320
Rule ID
SV-221231r612603_rule221231r508017_rule
Severity
Cat III
CCE
(None)
Group Title
SRG-APP-000247
CCI
CCI-001095
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practices strategies for setting tuning configurations. For message size restrictions, multiple places exist to set or override inbound or outbound message size. Failure to control the configuration strategy can result in loss of data or system availability. This setting enables the administrator to control the maximum message size on Receive connectors. Using connectors to control size limits may necessitate applying message size limitations in multiple places, with the potential of introducing conflicts and impediments in the mail flow. Changing this setting at the connector overrides the global one. Therefore, if operational needs require it, the connector value may be set lower than the global value with the rationale documented in the EDSP.

Fix Text

Update the EDSP to reflect the global maximum message receive size. Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -MaxMessageSize <'MaxReceiveSize'> Note: The <IdentityName> and <MaxReceiveSize> values must be in single quotes. or The value as identified by the EDSP that has obtained a signoff with risk acceptance.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the global maximum message receive size. Open the Exchange Management Shell and enter the following command: Identify Internet-facing connectors. Get-ReceiveConnector | Select Name, Identity, MaxMessageSize If the value of "MaxMessageSize" is not the same as the global value, this is a finding. or If "MaxMessageSize" is set to a numeric value different from the global value and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange messages with a blank sender field must be rejected.

Finding ID
EX16-ED-000330
Rule ID
SV-221232r612603_rule221232r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Anonymous email (messages with blank sender fields) cannot be replied to. Messages formatted in this way may be attempting to hide their true origin to avoid responses or to spam any receiver with impunity while hiding their source of origination. Rather than spend resources and risk infection while evaluating them, it is recommended that these messages be filtered immediately upon receipt and not forwarded to end users.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SenderFilterConfig -Action Reject

Check Content

This requirement is N/A for SIPR enclaves. This requirement is N/A if the organization subscribes to EEMSG or other similar DoD enterprise protections for email services. Open the Exchange Management Shell and enter the following command: Get-SenderFilterConfig | Select Name, Action If the value of "Action" is not set to "Reject", this is a finding.

Exchange messages with a blank sender field must be filtered.

Finding ID
EX16-ED-000340
Rule ID
SV-221233r612603_rule221233r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Anonymous email (messages with blank sender fields) cannot be replied to. Messages formatted in this way may be attempting to hide their true origin to avoid responses or to spam any receiver with impunity while hiding their source of origination. Rather than spend resources and risk infection while evaluating them, it is recommended that these messages be filtered immediately upon receipt and not forwarded to end users.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SenderFilterConfig -BlankSenderBlockingEnabled $true

Check Content

This requirement is N/A for SIPR enclaves. This requirement is N/A if the organization subscribes to EEMSG or other similar DoD enterprise protections for email services. Open the Exchange Management Shell and enter the following command: Get-SenderFilterConfig | Select Name, BlankSenderBlockingEnabled If the value of "BlankSenderBlockingEnabled" is not set to "True", this is a finding.

Exchange filtered messages must be archived.

Finding ID
EX16-ED-000350
Rule ID
SV-221234r612603_rule221234r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. This significantly reduces the attack vector for inbound email-borne spam and malware. As messages are filtered, it is prudent to temporarily host them in an archive for evaluation by administrators or users. The archive can be used to recover messages that might have been inappropriately filtered, preventing data loss, and to provide a base of analysis that can provide future filter refinements.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ContentFilterConfig -QuarantineMailbox <'QuarantineMailbox SmtpAddress'> Note: The <QuarantineMailbox SmtpAddress> value must be in single quotes.

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Open the Exchange Management Shell and enter the following command: Get-ContentFilterConfig | Select Name, QuarantineMailbox If no SMTP address is assigned to "QuarantineMailbox", this is a finding.

The Exchange Sender filter must block unaccepted domains.

Finding ID
EX16-ED-000360
Rule ID
SV-221235r612603_rule221235r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Spam origination sites and other sources of suspected email-borne malware have the ability to corrupt, compromise, or otherwise limit availability of email servers. Limiting exposure to unfiltered inbound messages can reduce the risk of spam and malware impacts. The Global Deny list blocks messages originating from specific sources. Most blacklist filtering is done using a commercial Block List service, because eliminating threats from known spammers prevents the messages being evaluated inside the enclave where there is more risk they can do harm. Additional sources should also be blocked to supplement the contents of the commercial Block List service. For example, during a zero-day threat action, entries can be added and then removed when the threat is mitigated. An additional best practice is to enter the enterprise’s home domains in the Deny List, because inbound email with a "from" address of the home domain is very likely to be spoofed spam.

Fix Text

Update the EDSP to reflect the unaccepted domains that are to be blocked. Open the Exchange Management Shell and enter the following command: For BlockedDomains: Set-SenderFilterConfig -BlockedDomains <BlockedDomain> Repeat the procedure for each domain that is to be blocked. or For BlockedDomainsAndSubdomains: Set-SenderFilterConfig -BlockedDomainsAndSubdomains <BlockedDomainAndSubdomain> Repeat the procedure for each domain and all of its subdomains that are to be blocked.

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Review the Email Domain Security Plan (EDSP). Determine the unaccepted domains that are to be blocked. Open the Exchange Management Shell and enter the following command: Get-SenderFilterConfig | Select Name, BlockedDomains, BlockedDomainsAndSubdomains If the value for "BlockedDomains" or "BlockedDomainsAndSubdomains" does not reflect the list of accepted domains, this is a finding.

Exchange nonexistent recipients must not be blocked.

Finding ID
EX16-ED-000370
Rule ID
SV-221236r612603_rule221236r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Spam originators, in an effort to refine mailing lists, sometimes use a technique where they first create fictitious names and then monitor rejected emails for non-existent recipients. Those not rejected are deemed to exist and are used in future spam mailings. To prevent this disclosure of existing email accounts to spammers, email to nonexistent recipients must not be blocked. Instead, it is recommended that all messages be received, then evaluated and disposed of without enabling the sender to determine existent vs. nonexistent recipients.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-RecipientFilterConfig -RecipientValidationEnabled $false

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Open the Exchange Management Shell and enter the following command: Get-RecipientFilterConfig | Select Name, RecipientValidationEnabled If the value of "RecipientValidationEnabled" is not set to "False", this is a finding.

The Exchange Sender Reputation filter must be enabled.

Finding ID
EX16-ED-000380
Rule ID
SV-221237r612603_rule221237r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Sender Reputation is antispam functionality that blocks messages according to many characteristics of the sender. Sender Reputation relies on persisted data about the sender to determine what action, if any, to take on an inbound message. This setting enables the Sender Reputation function.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SenderReputationConfig -Enabled $true

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Open the Exchange Management Shell and enter the following command: Get-SenderReputationConfig | Select Name, Enabled If the value of "Enabled" is not set to "True", this is a finding.

The Exchange Sender Reputation filter must identify the spam block level.

Finding ID
EX16-ED-000390
Rule ID
SV-221238r612603_rule221238r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Sender Reputation is antispam functionality that blocks messages according to many characteristics of the sender. Sender Reputation relies on persisted data about the sender to determine what action, if any, to take on an inbound message. This setting enables the threshold at which an email will be considered spam.

Fix Text

Update the EDSP to reflect the SrlBlockThreshold size. Open the Exchange Management Shell and enter the following command: Set-SenderReputationConfig -SrlBlockThreshold 6 or The value as identified by the EDSP that has obtained a signoff with risk acceptance.

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Review the Email Domain Security Plan (EDSP). Determine the SrlBlockThreshold value. Open the Exchange Management Shell and enter the following command: Get-SenderReputationConfig | Select Name, SrlBlockThreshold If the value of SrlBlockThreshold is not set to "6", this is a finding. or If the value of "SrlBlockThreshold" is set to a value other than "6" and has signoff and risk acceptance in the EDSP, this is not a finding.

Exchange Attachment filtering must remove undesirable attachments by file type.

Finding ID
EX16-ED-000400
Rule ID
SV-221239r612603_rule221239r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages are eliminated from the message stream rather than admitting them into the mail server environment. Attachments are being used more frequently for different forms of attacks. By filtering undesirable attachments, a large percent of malicious code can be prevented from entering the system. Attachments must be controlled at the entry point into the email environment to prevent successful attachment-based attacks. The following is a basic list of known attachments that should be filtered from Internet mail attachments: *.ade *.crt *.jse *.msi *.scr *.wsh *.dir *.adp *.csh *.ksh *.msp *.sct *.htm *.dcr *.app *.exe *.lnk *.mst *.shb *.html *.plg *.asx *.fxp *.mda *.ops *.shs *.htc *.spl *.bas *.hlp *.mdb *.pcd *.url *.mht *.swf *.bat *.hta *.mde *.pif *.vb *.mhtml *.zip *.chm *.inf *.mdt *.prf *.vbe *.shtm *.cmd *.ins *.mdw *.prg *.vbs *.shtml *.com *.isp *.mdz *.reg *.wsc *.stm *.cpl *.js *.msc *.scf *.wsf *.xml

Fix Text

Update the EDSP to reflect the list of undesirable attachment types that should be stripped. Open the Exchange Management Shell and enter the following command: Add-AttachmentFilterEntry -Name <'*.FileExtension'> -Type FileName Repeat the procedure for each undesirable attachment type.

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Review the Email Domain Security Plan (EDSP). Determine the list of undesirable attachment types that should be stripped. Open the Exchange Management Shell and enter the following command: Get-AttachmentFilterEntry For each attachment type, if the values returned are different from the EDSP documented attachment types, this is a finding.

The Exchange Spam Evaluation filter must be enabled.

Finding ID
EX16-ED-000410
Rule ID
SV-221240r612603_rule221240r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

By performing filtering at the perimeter, up to 90 percent of spam, malware, and other undesirable messages may be eliminated from the transport message stream, preventing their entry into the Exchange environment. This significantly reduces the attack vector for inbound email-borne spam and malware. Spam Evaluation filters scan inbound email messages for evidence of spam and other attacks that primarily use "social engineering" techniques. Upon evaluation completion, a rating is assigned to each message estimating the likelihood of its being spam. Upon arrival at the destination mailbox, the junk mail filter threshold (also configurable) determines whether the message will be withheld from delivery, delivered to the junk mail folder, or delivered to the user’s inbox.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ContentFilterConfig -Enabled $true

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Open the Exchange Management Shell and enter the following command: Get-ContentFilterConfig | Select Name, Identity, Enabled If the value of "Enabled" is not set to "True", this is a finding.

The Exchange Block List service provider must be identified.

Finding ID
EX16-ED-000420
Rule ID
SV-221241r612603_rule221241r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Block List filtering is a sanitization process performed on email messages prior to their arrival at the destination mailbox. By performing this process at the email perimeter, threats can be eliminated outside the enclave, where there is less risk for them to do harm. Block List services (sometimes called Reputation Data services) are fee-based data providers that collect the IP addresses of known spammers and other malware purveyors. Block List service subscribers benefit from more effective spam elimination. (Spam is estimated to compose up to 90 percent of inbound mail volume.) Failure to specify a Block List provider risks that manual email administration effort would be needed to maintain and update larger Block Lists than a single email site administrator could conveniently or accurately maintain. The Block List service vendor provides a value for this field, usually the Domain Name System (DNS) suffix for its domain.

Fix Text

Update the EDSP to reflect the name and information for the Block List provider. Open the Exchange Management Shell and enter the following command: Set-IPBlockListProvider -Name <Provider Name> [Additional optional parameters as required by the service provider]

Check Content

If not using a service provider, this requirement is not applicable. Review the Email Domain Security Plan (EDSP). Determine the name and information for the Block List provider. Open the Exchange Management Shell and enter the following command: Get-IPBlockListProvider | Select Name, Identity, LookupDomain If the values for "Name", GUID, and "LookupDomain" are not configured, this is a finding.

Exchange messages with a malformed From address must be rejected.

Finding ID
EX16-ED-000430
Rule ID
SV-221242r612603_rule221242r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Sender Identification (SID) is an email antispam sanitization process. Sender ID uses DNS MX record lookups to verify the Simple Mail Transfer Protocol (SMTP) sending server is authorized to send email for the originating domain. Failure to implement Sender ID risks that spam could be admitted into the email domain that originates from rogue servers. Most spam content originates from domains where the IP address has been spoofed prior to sending, thereby avoiding detection. For example, messages with malformed or incorrect "purported responsible sender" data in the message header could be (best case) created by using RFI noncompliant software but is more likely to be spam.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SenderIdConfig -SpoofedDomainAction Reject

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Open the Exchange Management Shell and enter the following command: Get-SenderIdConfig | Select Name, Identity, SpoofedDomainAction If the value of "SpoofedDomainAction" is not set to "Reject", this is a finding.

The Exchange Recipient filter must be enabled.

Finding ID
EX16-ED-000470
Rule ID
SV-221243r612603_rule221243r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-RecipientFilterConfig -Enabled $true

Check Content

Open the Exchange Management Shell and enter the following command: Get-RecipientFilterConfig | Select Name, Enabled If the value of "Enabled" is not set to "True", this is a finding.

The Exchange tarpitting interval must be set.

Finding ID
EX16-ED-000480
Rule ID
SV-221244r612603_rule221244r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Tarpitting is the practice of artificially delaying server responses for specific Simple Mail Transfer Protocol (SMTP) communication patterns that indicate high volumes of spam or other unwelcome messages. The intent of tarpitting is to slow down the communication process for spam batches to reduce the cost effectiveness of sending spam and thwart directory harvest attacks. A directory harvest attack is an attempt to collect valid email addresses from a particular organization so the email addresses can be added to a spam database. A program can be written to collect email addresses that return a "Recipient OK" SMTP response and discard all email addresses that return a "User unknown" SMTP response. Tarpitting makes directory harvest attacks too costly to automate efficiently.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -TarpitInterval '00:00:05' Note: The <IdentityName> value and the Interval must be in single quotes. Repeat the procedures for each Receive connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, TarpitInterval For each Receive connector, if the value of "TarpitInterval" is not set to "00:00:05" or greater, this is a finding.

Exchange internal Receive connectors must not allow anonymous connections.

Finding ID
EX16-ED-000490
Rule ID
SV-221245r612603_rule221245r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

This control is used to limit the servers that may use this server as a relay. If a Simple Mail Transport Protocol (SMTP) sender does not have a direct connection to the Internet (for example, an application that produces reports to be emailed), it will need to use an SMTP Receive connector that does have a path to the Internet (for example, a local email server) as a relay. SMTP relay functions must be protected so third parties are not able to hijack a relay service for their own purposes. Most commonly, relay hijacking is done by spammers to disguise the source of their messages and may also be used to cover the source of more destructive attacks. Relays can be restricted in one of three ways: by blocking relays (restrict to a blank list of servers); by restricting use to lists of valid servers; or by restricting use to servers that can authenticate. Because authenticated connections are the most secure for SMTP Receive connectors, it is recommended that relays allow only servers that can authenticate.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -PermissionGroups 'valid user group(s)' Note: The <IdentityName> value and user group(s) must be in single quotes. Example for user groups only: 'ExchangeServers, ExchangeUsers' Repeat the procedures for each Receive connector. This is an Example only: Set-ReceiveConnector -Identity <'IdentityName'> -PermissionGroups 'ExchangeUsers'

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, PermissionGroups For each Receive connector, if the value of "PermissionGroups" is "AnonymousUsers" for any non-Internet connector, this is a finding.

Exchange Simple Mail Transfer Protocol (SMTP) IP Allow List entries must be empty.

Finding ID
EX16-ED-000500
Rule ID
SV-221246r612603_rule221246r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Filters for messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective. Having items identified in the Allow List causes other spam evaluation steps to be bypassed and therefore should be used only with an abundance of caution. If spammers were to learn of entries in the Allow List, it could enable them to plan a denial of service attack (or other attack) by spoofing that source.

Fix Text

Update the EDSP to reflect the SMTP allow list settings. Open the Exchange Management Shell and enter the following command: Note: Remove any value(s) that are not identified by the EDSP or have not obtained a signoff with risk acceptance. Remove-IPAllowListEntry -Identity <IP Allow List entry ID>

Check Content

Review the Email Domain Security Plan (EDSP). Identify the SMTP allow list settings. Open the Exchange Management Shell and enter the following command: Get-IPAllowListEntry | fl If the result returns any values, this is a finding. or If the result returns any values but has signoff and risk acceptance in the EDSP, this is not a finding.

The Exchange Simple Mail Transfer Protocol (SMTP) IP Allow List Connection filter must be enabled.

Finding ID
EX16-ED-000510
Rule ID
SV-221247r612603_rule221247r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Filters for messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective. Having items identified in the Allow List causes other spam evaluation steps to be bypassed and therefore should be used only with an abundance of caution. If spammers were to learn of entries in the Allow List, it could enable them to plan a denial of service attack (or other attack) by spoofing that source.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-IPAllowListConfig -Enabled $true

Check Content

Open the Exchange Management Shell and enter the following command: Get-IPAllowListConfig | Select Name, Enabled If the value for "Enabled" is not set to "True", this is a finding.

The Exchange Simple Mail Transfer Protocol (SMTP) Sender filter must be enabled.

Finding ID
EX16-ED-000520
Rule ID
SV-221248r612603_rule221248r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Email system availability depends in part on best practices strategies for setting tuning configurations. Careful tuning reduces the risk that system or network congestion will contribute to availability impacts. Filters that govern inbound email evaluation can significantly reduce spam, phishing, and spoofed emails. Filters for messages from blank senders, known spammers, or zero-day attack modifications must be enabled to be effective. Failure to enable the filter will result in no action taken. This setting should always be enabled.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SenderFilterConfig -Enabled $true

Check Content

This requirement is N/A for SIPR enclaves. This requirement is N/A if the organization subscribes to EEMSG or other similar DoD enterprise protections for email services. Open the Exchange Management Shell and enter the following command: Get-SenderFilterConfig | Select Name, Enabled If the value of "Enabled" is not set to "True", this is a finding.

Exchange must have antispam filtering installed.

Finding ID
EX16-ED-000530
Rule ID
SV-221249r612603_rule221249r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Originators of spam messages are constantly changing their techniques in order to defeat spam countermeasures; therefore, spam software must be constantly updated to address the changing threat. Spam protection mechanisms include, for example, signature definitions, rule sets, and algorithms. Exchange 2016 provides both antispam and antimalware protection out of the box. The Exchange 2016 antispam and antimalware product capabilities are limited but still provide some protection.

Fix Text

Install the AntiSpam module. Open the Exchange Management Shell and enter the following command: & $env:ExchangeInstallPath\Scripts\Install-AntiSpamAgents.ps1

Check Content

Review the Email Domain Security Plan (EDSP) for an installed antispam product. Note: If using another DoD-approved antispam product for email or a DoD-approved Email Gateway spamming device, such as Enterprise Email Security Gateway (EEMSG), this is not applicable. Open the Exchange Management Shell and enter the following command: Get-ContentFilterConfig | Format-Table Name, Enabled If no value is returned, this is a finding.

Exchange must have antispam filtering enabled.

Finding ID
EX16-ED-000540
Rule ID
SV-221250r612603_rule221250r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Originators of spam messages are constantly changing their techniques in order to defeat spam countermeasures; therefore, spam software must be constantly updated to address the changing threat. Spam protection mechanisms include, for example, signature definitions, rule sets, and algorithms. Exchange 2016 provides both antispam and antimalware protection out of the box. The Exchange 2016 antispam and antimalware product capabilities are limited but still provide some protection.

Fix Text

Open the Exchange Management Shell and enter the following command for any values that were not set to True: Set-ContentFilterConfig -Enabled $true Set-SenderFilterConfig -Enabled $true Set-SenderIDConfig -Enabled $true Set-SenderReputationConfig -Enabled $true

Check Content

Review the Email Domain Security Plan (EDSP) for an installed antispam product. Note: If using another DoD-approved antispam product for email or a DoD-approved Email Gateway spamming device, such as Enterprise Email Security Gateway (EEMSG), this is not applicable. Open the Exchange Management Shell and enter the following command: Get-ContentFilterConfig | Format-Table Name, Enabled; Get-SenderFilterConfig | Format-Table Name, Enabled; Get-SenderIDConfig | Format-Table Name, Enabled; Get-SenderReputationConfig | Format-Table Name, Enabled If any of the following values returned are not set to "True", this is a finding: Set-ContentFilterConfig Set-SenderFilterConfig Set-SenderIDConfig Set-SenderReputationConfig

Exchange must have antispam filtering configured.

Finding ID
EX16-ED-000550
Rule ID
SV-221251r612603_rule221251r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Originators of spam messages are constantly changing their techniques in order to defeat spam countermeasures; therefore, spam software must be constantly updated to address the changing threat. A manual update procedure is labor intensive and does not scale well in an enterprise environment. This risk may be mitigated by using an automatic update capability. Spam protection mechanisms include, for example, signature definitions, rule sets, and algorithms. Exchange 2016 provides both antispam and antimalware protection out of the box. The Exchange 2016 antispam and antimalware product capabilities are limited but still provide some protection.

Fix Text

Following vendor best practice guidance, install and configure a DoD approved scanner.

Check Content

Site should utilize an approved DoD scanner as Exchange Malware software has a limited scanning capability. If an approved DoD scanner is not being used, this is a finding.

Exchange Sender Identification Framework must be enabled.

Finding ID
EX16-ED-000560
Rule ID
SV-221252r612603_rule221252r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Email is only as secure as the recipient. When the recipient is an email server accepting inbound messages, authenticating the sender enables the receiver to better assess message quality and to validate the sending domain as authentic. One or more authentication techniques used in combination can be effective in reducing spam, phishing, and forger attacks. The Sender ID Framework (SIDF) receiver accesses specially formatted DNS records (SPF format) that contain the IP address of authorized sending servers for the sending domain that can be compared to data in the email message header. Receivers are able to validate the authenticity of the sending domain, helping to avoid receiving inbound messages from phishing or other spam domains.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SenderIdConfig -Enable $true

Check Content

Note: If third-party anti-spam product is being used, the anti-spam product must be configured to meet the requirement. Open the Exchange Management Shell and enter the following command: Get-SenderIdConfig | Select Name, Identity, Enabled If the value of "Enabled" is not set to "True", this is a finding.

Exchange must renderstrip hyperlinkshyperlink from email sources from non-.mil domains as unclickable.

Finding ID
EX16-ED-000570
Rule ID
SV-221253r612603_rule221253r508017_rule
Severity
Cat I
CCE
(None)
Group Title
SRG-APP-000261
CCI
CCI-001308
Target Key
(None)
Documentable
No
Discussion

Active hyperlinks within an email are susceptible to attacks of malicious software or malware. The hyperlink could lead to a malware infection or redirect the website to another fraudulent website without the user's consent or knowledge. Exchange does not have a built-in message filtering capability. DoD Enterprise Email (DEE) has created a custom resolution to filter messages from non-.mil users that have hyperlinks in the message body. The hyperlink within the messages will be modified, preventing end users from automatically clicking links.

Fix Text

Update the EDSP to reflect the name of the Transport Agent. Contact the DISA Enterprise Email Service Desk at disa.tinker.eis.mbx.dod-enterprise-services-service-desk@mail.mil and request the Agent and installation procedures. or Contact DEE Engineering PMO and request the Agent and installation procedures.

Check Content

Note: If using another DoD-approved antispam product for email or a DoD-approved Email Gateway spamming device, such as Enterprise Email Security Gateway (EEMSG), this is not applicable. Note: If system is on SIPRNet, this is not applicable. Review the Email Domain Security Plan (EDSP). Determine the name of the Transport Agent. Open the Windows PowerShell console and enter the following command: Get-TransportAgent -Name 'customAgent' | FL If the value does not return "customAgent", this is a finding. Note: "customAgent" is the name of the custom agent developed to renderstrip hyperlink email sources from non .mil domains asand unclickable.must be in single quot

The Exchange application directory must be protected from unauthorized access.

Finding ID
EX16-ED-000580
Rule ID
SV-221254r612603_rule221254r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000378
CCI
CCI-001812
Target Key
(None)
Documentable
No
Discussion

Default product installations may provide more generous access permissions than are necessary to run the application. By examining and tailoring access permissions to more closely provide the least amount of privilege possible, attack vectors that align with user permissions are less likely to access more highly secured areas.

Fix Text

Update the EDSP to reflect the authorized groups and users that have access to the Exchange application directories. Navigate to the Exchange application directory and remove or modify the group or user access permissions. Note: The default installation directory is \Program Files\Microsoft\Exchange Server\V15.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the authorized groups and users that have access to the Exchange application directories. Determine if the access permissions on the directory match the access permissions listed in the EDSP. If any group or user has different access permissions than listed in the EDSP, this is a finding. Note: The default installation directory is \Program Files\Microsoft\Exchange Server\V15.

The Exchange software baseline copy must exist.

Finding ID
EX16-ED-000590
Rule ID
SV-221255r612603_rule221255r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000380
CCI
CCI-001813
Target Key
(None)
Documentable
No
Discussion

Exchange software, as with other application software installed on a host system, must be included in a system baseline record and periodically reviewed; otherwise, unauthorized changes to the software may not be discovered. This effort is a vital step to securing the host and the applications, as it is the only method that may provide the ability to detect and recover from otherwise undetected changes, such as those that result from worm or bot intrusions. The Exchange software and configuration baseline is created and maintained for comparison during scanning efforts. Operational procedures must include baseline updates as part of configuration management tasks that change the software and configuration.

Fix Text

Implement an email software baseline process and update the EDSP.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the baseline documentation. Review the application software baseline procedures and implementation artifacts. Note the list of files and directories included in the baseline procedure for completeness. If an email software copy exists to serve as a baseline and is available for comparison during scanning efforts, this is not a finding.

Exchange services must be documented and unnecessary services must be removed or disabled.

Finding ID
EX16-ED-000610
Rule ID
SV-221256r612603_rule221256r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000383
CCI
CCI-001762
Target Key
(None)
Documentable
No
Discussion

Unneeded but running services offer attackers an enhanced attack profile, and attackers are constantly watching to discover open ports with running services. By analyzing and disabling unneeded services, the associated open ports become unresponsive to outside queries, and servers become more secure as a result. Exchange Server has role-based server deployment to enable protocol path control and logical separation of network traffic types. For example, a server implemented in the Client Access role (i.e., Outlook Web App [OWA]) is configured and tuned as a web server using web protocols. A client access server exposes only web protocols (HTTP/HTTPS), enabling system administrators to optimize the protocol path and disable all services unnecessary for Exchange web services. Similarly, servers created to host mailboxes are dedicated to that task and must operate only the services needed for mailbox hosting. (Exchange servers must also operate some web services, but only to the degree that Exchange requires the IIS engine in order to function). Because POP3 and IMAP4 clients are not included in the standard desktop offering, they must be disabled.

Fix Text

Update the EDSP with the services required for the system to function. Navigate to Administrator Tools >> Services and disable or remove any services that are not required.

Check Content

Review the Email Domain Security Plan (EDSP). Note: Required services will vary between organizations and will vary depending on the role of the individual system. Organizations will develop their own list of services, which will be documented and justified with the ISSO. The site’s list will be provided for any security review. Services that are common to multiple systems can be addressed in one document. Exceptions for individual systems should be identified separately by system. Open a Windows PowerShell and enter the following command: Get-Service | Where-Object {$_.status -eq 'running'} Note: The command returns a list of installed services and the status of that service. If the services required are not documented in the EDSP or undocumented or unnecessary services are running, this is a finding.

Exchange software must be installed on a separate partition from the OS.

Finding ID
EX16-ED-000620
Rule ID
SV-221257r612603_rule221257r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000431
CCI
CCI-002530
Target Key
(None)
Documentable
No
Discussion

In the same way that added security layers can provide a cumulative positive effect on security posture, multiple applications can provide a cumulative negative effect. A vulnerability and subsequent exploit to one application can lead to an exploit of other applications sharing the same security context. For example, an exploit to a web server process that leads to unauthorized administrative access to the host system can most likely lead to a compromise of all applications hosted by the same system. Email services should be installed on a partition that does not host other applications. Email services should never be installed on a Domain Controller/Directory Services server.

Fix Text

Update the EDSP to reflect the directory where Exchange is installed. Install Exchange on a dedicated application directory or partition separate than that of the OS.

Check Content

Review the Email Domain Security Plan (EDSP). Determine the directory where Exchange is installed. Open Windows Explorer. Navigate to the location where Exchange is installed. If Exchange resides on a directory or partition other than that of the OS and does not have other applications installed (without associated approval from the ISSO), this is not a finding.

The Exchange SMTP automated banner response must not reveal server details.

Finding ID
EX16-ED-000630
Rule ID
SV-221258r612603_rule221258r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000435
CCI
CCI-002385
Target Key
(None)
Documentable
No
Discussion

Automated connection responses occur as a result of FTP or Telnet connections when connecting to those services. They report a successful connection by greeting the connecting client and stating the name, release level, and (often) additional information about the responding product. While useful to the connecting client, connection responses can also be used by a third party to determine operating system or product release levels on the target server. The result can include disclosure of configuration information to third parties, paving the way for possible future attacks. For example, when querying the SMTP service on port 25, the default response looks similar to this one: 220 exchange.mydomain.org Microsoft ESMTP MAIL Service, Version: 6.0.3790.211 ready at Wed, 2 Feb 2005 23:40:00 -0500 Changing the response to hide local configuration details reduces the attack profile of the target.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -Banner '220 SMTP Server Ready' Note: The <IdentityName> and 220 SMTP Server Ready values must be in single quotes.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, Banner If the value of "Banner" is not set to "220 SMTP Server Ready", this is a finding.

Exchange must provide redundancy.

Finding ID
EX16-ED-000660
Rule ID
SV-221259r612603_rule221259r508017_rule
Severity
Cat I
CCE
(None)
Group Title
SRG-APP-000435
CCI
CCI-002418
Target Key
(None)
Documentable
No
Discussion

Denial of Service (DoS) is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity. This requirement addresses the configuration of applications to mitigate the impact of DoS attacks that have occurred or are ongoing on application availability. For each application, known and potential DoS attacks must be identified and solutions for each type implemented. A variety of technologies exist to limit or, in some cases, eliminate the effects of DoS attacks (e.g., limiting processes or restricting the number of sessions the application opens at one time). Employing increased capacity and bandwidth, combined with service redundancy, may reduce the susceptibility to some DoS attacks.

Fix Text

Update the EDSP to reflect the Exchange servers used for redundancy. Configure two or more Edge servers for load balancing.

Check Content

Review the Email Domain Security Plan (EDSP). Determine if the Exchange servers are using redundancy by entering the following command: Get-TransportService | select FL If the value returned is not at least two Edge servers, this is a finding.

Exchange internal Send connectors must use an authentication level.

Finding ID
EX16-ED-000670
Rule ID
SV-221260r612603_rule221260r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000435
CCI
CCI-002385
Target Key
(None)
Documentable
No
Discussion

The Simple Mail Transfer Protocol (SMTP) connector is used by Exchange to send and receive messages from server to server. Several controls work together to provide security between internal servers. This setting controls the encryption method used for communications between servers. With this feature enabled, only servers capable of supporting Transport Layer Security (TLS) will be able to send and receive mail within the domain. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from server to server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption can be compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between servers.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'IdentityName'> -TlsAuthLevel DomainValidation

Check Content

Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, TlsAuthLevel If the value of "TlsAuthLevel" is not set to "DomainValidation", this is a finding.

Exchange internal Receive connectors must require encryption.

Finding ID
EX16-ED-000680
Rule ID
SV-221261r612603_rule221261r508017_rule
Severity
Cat I
CCE
(None)
Group Title
SRG-APP-000439
CCI
CCI-002418
Target Key
(None)
Documentable
No
Discussion

The Simple Mail Transfer Protocol (SMTP) Receive connector is used by Exchange to send and receive messages from server to server using SMTP protocol. This setting controls the encryption strength used for client connections to the SMTP Receive connector. With this feature enabled, only clients capable of supporting secure communications will be able to send mail using this SMTP server. Where secure channels are required, encryption can also be selected. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from the client to the server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption have been compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between the client and server.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-ReceiveConnector -Identity <'IdentityName'> -AuthMechanism 'Tls' Note: The <IdentityName> value must be in single quotes. Repeat the process for each Receive connector.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ReceiveConnector | Select Name, Identity, AuthMechanism For each Receive connector, if the value of "AuthMechanism" is not set to "Tls", this is a finding.

Exchange internal Send connectors must require encryption.

Finding ID
EX16-ED-000690
Rule ID
SV-221262r612603_rule221262r508017_rule
Severity
Cat I
CCE
(None)
Group Title
SRG-APP-000439
CCI
CCI-002418
Target Key
(None)
Documentable
No
Discussion

The Simple Mail Transfer Protocol (SMTP) connector is used by Exchange to send and receive messages from server to server. Several controls work together to provide security between internal servers. This setting controls the encryption method used for communications between servers. With this feature enabled, only servers capable of supporting Transport Layer Security (TLS) will be able to send and receive mail within the domain. The use of secure communication prevents eavesdroppers from reading or modifying communications between mail clients and servers. While sensitive message bodies should be encrypted by the sender at the client, requiring a secure connection from server to server adds protection by encrypting the sender and recipient information that cannot be encrypted by the sender. Individually, channel security and encryption can be compromised by attackers. Used together, email becomes a more difficult target, and security is heightened. Failure to enable this feature gives eavesdroppers an opportunity to read or modify messages between servers.

Fix Text

Open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'IdentityName'> -TlsDomain <'SMTP Domain'> Set-SendConnector -Identity <'ReceiveConnector'> -DomainSecureEnabled 'True' Note: The SMTP Domain is the internal SMTP domain within the organization.

Check Content

Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, TlsDomain If the value of "TlsDomain" is not set to the value of the internal <'SMTP Domain'>, this is a finding. Get-SendConnector | Select Name, Identity, DomainSecureEnabled If the value of 'DomainSecureEnabled' is not set to 'True', this is a finding.

Exchange must have the most current, approved service pack installed.

Finding ID
EX16-ED-000700
Rule ID
SV-221263r612603_rule221263r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000456
CCI
CCI-002605
Target Key
(None)
Documentable
No
Discussion

The organization (including any contractor to the organization) must promptly install security-relevant software updates (e.g., patches, service packs, hot fixes). Flaws discovered during security assessments, continuous monitoring, incident response activities, or information system error handling must also be addressed.

Fix Text

Install the most current, approved service pack.

Check Content

Open the Exchange Management Shell and enter the following command: Get-ExchangeServer | fl name, AdminDisplayVersion If the value of "AdminDisplayVersion" does not return the most current, approved service pack, this is a finding.

The application must configure malicious code protection mechanisms to perform periodic scans of the information system every seven days.

Finding ID
EX16-ED-000720
Rule ID
SV-221264r612603_rule221264r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000277
CCI
CCI-001241
Target Key
(None)
Documentable
No
Discussion

Malicious code protection mechanisms include, but are not limited, to anti-virus and malware detection software. In order to minimize potential negative impact to the organization that can be caused by malicious code, it is imperative that malicious code is identified and eradicated. Malicious code includes viruses, worms, trojan horses, and spyware. It is not enough to simply have the software installed; this software must periodically scan the system to search for malware on an organization-defined frequency. This requirement applies to applications providing malicious code protection.

Fix Text

Open the Exchange Management Shell and enter the following command: & env:ExchangeInstallPath\Scripts\Disable-Antimalwarescanning.ps1

Check Content

Open the Exchange Management Shell and enter the following command: Get-TransportAgent "Malware Agent" If the value of "Enabled" is set to "True", this is a finding.

The application must configure malicious code protection mechanisms to perform periodic scans of the information system every seven days.

Finding ID
EX16-ED-000730
Rule ID
SV-221265r612603_rule221265r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000277
CCI
CCI-001241
Target Key
(None)
Documentable
No
Discussion

Malicious code protection mechanisms include, but are not limited, to anti-virus and malware detection software. In order to minimize potential negative impact to the organization that can be caused by malicious code, it is imperative that malicious code is identified and eradicated. Malicious code includes viruses, worms, trojan horses, and spyware. It is not enough to simply have the software installed; this software must periodically scan the system to search for malware on an organization-defined frequency. This requirement applies to applications providing malicious code protection.

Fix Text

Following vendor best practice guidance, install and configure a third-party malicious code protection application.

Check Content

Site must utilize an approved DoD third-party malicious code scanner. Consult with System Administrator to demonstrate the application being used to provide malicious code protection in the Exchange implementation. If System Administrator is unable to demonstrate a third-party malicious code protection application, this is a finding. If System Administrator is unaware of a third-party malicious code protection application, this is a finding.

The application must be configured to block and quarantine malicious code upon detection, then send an immediate alert to appropriate individuals.

Finding ID
EX16-ED-000750
Rule ID
SV-221266r612603_rule221266r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000279
CCI
CCI-001243
Target Key
(None)
Documentable
No
Discussion

Malicious code protection mechanisms include, but are not limited, to anti-virus and malware detection software. In order to minimize potential negative impact to the organization that can be caused by malicious code, it is imperative that malicious code is identified and eradicated. Applications providing this capability must be able to perform actions in response to detected malware. Responses include blocking, quarantining, deleting, and alerting. Other technology- or organization-specific responses may also be employed to satisfy this requirement. Malicious code includes viruses, worms, trojan horses, and spyware. This requirement applies to applications providing malicious code protection.

Fix Text

Open the Exchange Management Shell and enter the following command: & env:ExchangeInstallPath\Scripts\Disable-Antimalwarescanning.ps1

Check Content

Open the Exchange Management Shell and enter the following command: Get-TransportAgent "Malware Agent" If the value of "Enabled" is set to "True", this is a finding.

The application must be configured to block and quarantine malicious code upon detection, then send an immediate alert to appropriate individuals.

Finding ID
EX16-ED-000760
Rule ID
SV-221267r612603_rule221267r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000279
CCI
CCI-001243
Target Key
(None)
Documentable
No
Discussion

Malicious code protection mechanisms include, but are not limited, to anti-virus and malware detection software. In order to minimize potential negative impact to the organization that can be caused by malicious code, it is imperative that malicious code is identified and eradicated. Applications providing this capability must be able to perform actions in response to detected malware. Responses include blocking, quarantining, deleting, and alerting. Other technology- or organization-specific responses may also be employed to satisfy this requirement. Malicious code includes viruses, worms, trojan horses, and spyware. This requirement applies to applications providing malicious code protection.

Fix Text

Following vendor best practice guidance, install and configure a third-party malicious code protection application.

Check Content

Site must utilize an approved DoD third-party malicious code scanner. Consult with System Administrator to demonstrate the application being used to provide malicious code protection in the Exchange implementation. If System Administrator is unable to demonstrate a third-party malicious code protection application, this is a finding. If System Administrator is unaware of a third-party malicious code protection application, this is a finding.

The application must update malicious code protection mechanisms whenever new releases are available in accordance with organizational configuration management policy and procedures.

Finding ID
EX16-ED-002400
Rule ID
SV-221268r612603_rule221268r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000276
CCI
CCI-001240
Target Key
(None)
Documentable
No
Discussion

Malicious code includes viruses, worms, trojan horses, and spyware. The code provides the ability for a malicious user to read from and write to files and folders on a computer's hard drive. Malicious code may also be able to run and attach programs, which may allow the unauthorized distribution of malicious mobile code. Once this code is installed on endpoints within the network, unauthorized users may be able to breach firewalls and gain access to sensitive data. This requirement applies to applications providing malicious code protection. Malicious code protection mechanisms include, but are not limited, to, anti-virus and malware detection software. Malicious code protection mechanisms (including signature definitions and rule sets) must be updated when new releases are available.

Fix Text

Open the Exchange Management Shell and enter the following command: & env:ExchangeInstallPath\Scripts\Disable-Antimalwarescanning.ps1

Check Content

Open the Exchange Management Shell and enter the following command: Get-TransportAgent "Malware Agent" If the value of "Enabled" is set to "True", this is a finding.

The application must update malicious code protection mechanisms whenever new releases are available in accordance with organizational configuration management policy and procedures.

Finding ID
EX16-ED-002410
Rule ID
SV-221269r612603_rule221269r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000276
CCI
CCI-001240
Target Key
(None)
Documentable
No
Discussion

Malicious code includes viruses, worms, trojan horses, and spyware. The code provides the ability for a malicious user to read from and write to files and folders on a computer's hard drive. Malicious code may also be able to run and attach programs, which may allow the unauthorized distribution of malicious mobile code. Once this code is installed on endpoints within the network, unauthorized users may be able to breach firewalls and gain access to sensitive data. This requirement applies to applications providing malicious code protection. Malicious code protection mechanisms include, but are not limited, to, anti-virus and malware detection software. Malicious code protection mechanisms (including signature definitions and rule sets) must be updated when new releases are available.

Fix Text

Following vendor best practice guidance, install and configure a third-party malicious code protection application.

Check Content

Site must utilize an approved DoD third-party malicious code scanner. Consult with System Administrator to demonstrate the application being used to provide malicious code protection in the Exchange implementation. If System Administrator is unable to demonstrate a third-party malicious code protection application, this is a finding. If System Administrator is unaware of a third-party malicious code protection application, this is a finding.

The applications built-in Malware Agent must be disabled.

Finding ID
EX16-ED-003010
Rule ID
SV-221270r612603_rule221270r508017_rule
Severity
Cat II
CCE
(None)
Group Title
SRG-APP-000278
CCI
CCI-001242
Target Key
(None)
Documentable
No
Discussion

Malicious code protection mechanisms include, but are not limited, to, anti-virus and malware detection software. In order to minimize potential negative impact to the organization that can be caused by malicious code, it is imperative that malicious code is identified and eradicated. Malicious code includes viruses, worms, trojan horses, and spyware. It is not enough to simply have the software installed; this software must periodically scan the system to search for malware on an organization-defined frequency. Exchange's built-in Malware Agent is not designed to address all malicious code protection workloads. This workload is best handled by third-party anti-virus and intrusion prevention software. Site must utilize an approved DoD scanner. Exchange Malware software has a limited scanning capability and does not scan files that are downloaded, opened, or executed.

Fix Text

Open the Exchange Management Shell and enter the following command: & env:ExchangeInstallPath\Scripts\Disable-Antimalwarescanning.ps1

Check Content

Open the Exchange Management Shell and enter the following command: Get-TransportAgent "Malware Agent" If the value of "Enabled" is set to "True", this is a finding.