CVE-2026-76166 Red Hat CVE debrief

Who should care

Defenders responsible for systems using mod_cluster should assess exposure and prioritize verification and potential remediation. This includes operators, platform administrators, vulnerability management teams, and security teams who need to evaluate the potential impact on their systems and take appropriate actions to mitigate the vulnerability.

Why it matters

CVE-2026-76166 is a medium-severity vulnerability in mod_cluster's AdvertiseListenerImpl that can cause a denial of service. Defenders should verify exposure, especially in systems using mod_cluster, and prioritize remediation based on the system's specific configuration and exposure.

• Potential denial of service due to advertise listener thread termination
• Need to verify mod_cluster usage and assess system exposure
• Possible silent failure without clear indication of the issue

Technical summary

The AdvertiseListenerImpl in mod_cluster's core module does not handle a crafted UDP multicast datagram correctly, leading to a NullPointerException that terminates the advertise listener thread. This vulnerability affects systems using mod_cluster and can cause a denial of service. Defenders should prioritize verifying exposure and assessing the impact of this vulnerability on their systems, especially those using mod_cluster. The failure is silent and persists until the node is restarted, making it crucial to review system logs and assess system exposure.

Defensive priority

Defenders should prioritize verifying exposure and assessing the impact of this vulnerability on their systems, especially those using mod_cluster.

Recommended defensive actions

• Verify if the mod_cluster component is used in the environment
• Assess the network exposure of systems using mod_cluster
• Review system logs for signs of the NullPointerException
• Consider applying patches or updates provided by the vendor
• Track exceptions and retest remediated assets
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Review compensating controls for exposed systems while remediation is scheduled and verified

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but the scope of affected systems and versions is not explicitly stated. Defenders should verify if the mod_cluster component is used in their environment, assess the network exposure of systems using mod_cluster, and review system logs for signs of the NullPointerException. The AdvertiseListenerImpl in mod_cluster's core module does not handle a crafted UDP multicast datagram correctly, leading to a NullPointerException that terminates the advertise listener thread.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.