The EBC is NOT configured to filter inbound AS-SIP-TLS traffic based on the IP addresses of the internal LSC(s) (or MFSS) OR the IP addresses of the EBCs fronting its authorized signaling partners as part of a layered defense.

From Voice/Video over Internet Protocol (VVoIP) STIG

Part of Deficient EBC config: AS-SIP-TLS source filtering

Associated with IA controls: ECSC-1

SV-21806r1_rule The EBC is NOT configured to filter inbound AS-SIP-TLS traffic based on the IP addresses of the internal LSC(s) (or MFSS) OR the IP addresses of the EBCs fronting its authorized signaling partners as part of a layered defense.

Vulnerability discussion

The EBC is in the VVoIP signaling between the LSC and MFSS. To limit its exposure to compromise and DOS, it must only exchange signaling messages using the designated protocol (AS-SIP-TLS) with the LSC(s) within the enclave and the EBC fronting the MFSS (and its backup) to which the LSC is assigned. Similarly, an EBC fronting an MFSS must only exchange signaling messages with the MFSS and LSC(s) within the enclave and the EBCs fronting other MFSSs and the LSCs that are assigned to it. While the EBC is also required to authenticate the source and integrity of the signaling packets it receives, filtering on source IP address adds a layer of protection for the MFSS. This is also a backup measure in the event this filtering is not done on the CER.Internal to the enclave, filtering signaling traffic based on the IP address(es) of the LSC(s) within the enclave limits the ability of rogue EIs attempting to establish calls or cause a DOS.

Check content

Inspect the configurations of the EBC to determine compliance with the requirement. This is a finding in the event the EBC does not filter inbound AS-SIP-TLS traffic based on the IP address(es) of the EBCs fronting authorized LSCs and MFSSs OR the EBC does not filter outbound AS-SIP-TLS traffic based on the IP address(es) of the LSC(s) within the enclave.

Fix text

Ensure the DISN NIPRNet IPVS firewall (EBC) is configured to only communicate as follows: > Within the enclave, ensure the EBC only establishes an AS-SIP-TLS session with the primary or backup LSC or the MFSS and its backup LSC within the enclave. >If the EBC is at a site without a MFSS: External to the enclave (across the WAN), ensure the EBC only establishes an AS-SIP-TLS session with the EBC at the enclave’s assigned primary and secondary (backup) MFSS sites. > If the EBC is at a MFSS site: External to the enclave (across the WAN), ensure the EBC only establishes an AS-SIP-TLS session with EBCs located at other MFSS sites and the LSC sites assigned to it.

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