The firewall must fail closed if the firewall filtering function is nonfunctional.

From Firewall Security Requirements Guide

Associated with: CCI-001190

SV-94117r1_rule The firewall must fail closed if the firewall filtering function is nonfunctional.

Vulnerability 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.

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.

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.

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