CMMCDocs.comCM.L2-3.4.8
Also known as: Application allowlisting requirement
The NIST SP 800-171 requirement that mandates application execution policies to prevent unauthorized software from running on in-scope systems.
CM.L2-3.4.8 requires the contractor to 'apply deny-by-exception (blacklisting) policy to prevent the use of unauthorized software or deny-all, permit-by-exception (whitelisting) policy to allow the execution of authorized software.' In CMMC practice, allowlisting (deny-all, permit-by-exception) is the strongly preferred approach.
Application allowlisting is one of the harder NIST SP 800-171 requirements to fully implement, especially in environments with diverse software needs. It requires a mechanism (Microsoft AppLocker, WDAC, third-party tools) that defines exactly which executables are permitted and blocks everything else.
A C3PAO will ask for the allowlist itself, the deployment evidence, and a demonstration that an unauthorized executable is actually blocked. This is one of the most common requirements to end up on a POA&M.
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