Free DISA STIG and SRG Library | Vaulted


The host running a BIND 9.X implementation must implement a set of firewall rules that restrict traffic on the DNS interface.

Finding ID
Rule ID
Cat II
Group Title
Target Key

Configuring hosts that run a BIND 9.X implementation to only accept DNS traffic on a DNS interface allows a system firewall to be configured to limit the allowed incoming ports/protocols to 53/tcp and 53/udp. Sending outgoing DNS messages from a random port minimizes the risk of an attacker guessing the outgoing message port and sending forged replies. The TCP/IP stack in DNS hosts (stub resolver, caching/resolving/recursive name server, authoritative name server, etc.) could be subjected to packet flooding attacks (such as SYNC and smurf), resulting in disruption of communication. By implementing a specific set of firewall rules that limit accepted traffic to the interface, these risk of packet flooding and other TCP/IP based attacks is reduced.

Fix Text

Configure the OS firewall to only allow incoming DNS traffic on ports 53/tcp and 53/udp. Add the following rules to the host firewall rule set: # iptables -A INPUT -i [DNS Interface] -p tcp --dport 53 -j ACCEPT # iptables -A INPUT -i [DNS Interface] -p udp --dport 53 -j ACCEPT # iptables -A INPUT -i [DNS Interface] -j DROP Note: If the system is not using an IPTables firewall, the appropriate firewall rules that limit traffic to ports 53/tcp and 53/udp should be configured on the active firewall.

Check Content

With the assistance of the DNS administrator, verify that the OS firewall is configured to only allow incoming messages on ports 53/tcp and 53/udp. Note: The following rules are for the IPTables firewall. If the system is utilizing a different firewall, the rules may be different. Inspect the hosts firewall rules for the following rules: -A INPUT -i [DNS Interface] -p tcp --dport 53 -j ACCEPT -A INPUT -i [DNS Interface] -p udp --dport 53 -j ACCEPT -A INPUT -i [DNS Interface] -j DROP If any of the above rules do not exist, this is a finding. If there are rules listed that allow traffic on ports other than 53/tcp and 53/udp, this is a finding.