Reports the specific build number of the firewall kernel module running on this gateway, a finer-grained identifier than the major or minor version. This is the number support engineers actually ask for when diagnosing a kernel-level bug, since a specific fix or regression is often tied to an exact build rather than the broader version number, and different gateways in the same cluster ending up on different builds after an inconsistent patch rollout is itself a troubleshooting lead. Example: two cluster members reporting different fwKernelBuild values despite matching fwVerMajor and fwVerMinor reveals an incomplete or inconsistent hotfix rollout between them.