V-79411
The firewall must fail closed if the firewall filtering function is nonfunctional.
Discussion
While failure to an open state may ensure users are not inconvenienced, it also circumvents a critical security network function that guards against direct and indirect network attacks. Allow traffic to flow without filtering or inspection puts the entire network and DoD critical assets at immediate risk. An example is a network element that blocks all traffic rather than allowing all traffic when a network element component fails (e.g., fail closed and do not forward traffic). This prevents an attacker from forcing a failure of the system in order to obtain access.
Fix Text
Configure the firewall to fail closed. The firewall must block all traffic rather than allowing all traffic when a network element component fails (e.g., fail closed and do not forward traffic). The recommended architecture is to implement load balancing so that the failure of the firewall redirects traffic to another filtering device. Obtain a risk acceptance in order to fail open.
Check Content
Review the firewall configuration to verify traffic flow defaults to closed when the firewall filtering function aborts or is nonfunctional. If the firewall is configured to allow traffic flow to attached interfaces when the firewall filtering function is non-functional, this is a finding.