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medium · CVSS 4.3

CVE-2026-76166

Modcluster-core: mod_cluster advertise listener: unauthenticated dos via crafted multicast datagram

Published 19 Aug 2026 · Source updated 3 Nov 2026 · Retrieved 2026-11-04 23:01 UTC

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What happened?

A flaw was found in mod_cluster's AdvertiseListenerImpl (org.jboss.modcluster core module). A single crafted UDP multicast datagram with a valid HTTP status line and a "Server:" header but without the "Date:", "Digest:", and "Sequence:" headers triggers a NullPointerException in verifyDigest() that is not caught by the worker thread's exception handler. This causes the advertise listener thread to terminate permanently. The failure is silent (isListening() continues to return true) and persists until the node is restarted. The crash occurs before the AdvertiseSecurityKey comparison, so deployments with a configured security key are still affected.

Description supplied by CVE Program. Formatting is simplified; follow the original advisory for full details.

Affected software and versions

Source-provided software and version information
SoftwareVersion informationFixed version
mod_cluster-coreRed HatDefault status: unaffectedSee vendor advisory
jws7-mod_clusterRed Hatunaffected: 0:2.1.1-1.Final_redhat_00001.1.el10jws to < *See vendor advisory
jws7-tomcatRed Hatunaffected: 0:11.0.21-10.redhat_00010.1.el10jws to < *See vendor advisory
jws7-tomcat-nativeRed Hatunaffected: 0:1.3.7-4.redhat_4.el10jws to < *See vendor advisory
jws7-mod_clusterRed Hatunaffected: 0:2.1.1-1.Final_redhat_00001.1.el8jws to < *See vendor advisory
jws7-tomcatRed Hatunaffected: 0:11.0.21-10.redhat_00010.1.el8jws to < *See vendor advisory
jws7-tomcat-nativeRed Hatunaffected: 0:1.3.7-4.redhat_4.el8jws to < *See vendor advisory
jws7-mod_clusterRed Hatunaffected: 0:2.1.1-1.Final_redhat_00001.1.el9jws to < *See vendor advisory
jws7-tomcatRed Hatunaffected: 0:11.0.21-10.redhat_00010.1.el9jws to < *See vendor advisory
jws7-tomcat-nativeRed Hatunaffected: 0:1.3.7-4.redhat_4.el9jws to < *See vendor advisory
mod_cluster-coreRed HatDefault status: affectedSee vendor advisory
mod_cluster-coreRed HatDefault status: affectedSee vendor advisory
mod_cluster-coreRed HatDefault status: affectedSee vendor advisory
mod_cluster-coreRed HatDefault status: unknownSee vendor advisory
mod_cluster-coreRed HatDefault status: affectedSee vendor advisory
mod_cluster-coreRed HatDefault status: affectedSee vendor advisory

Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.

Is it being exploited?

This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.

CISA data retrieved 2026-11-06 16:38 UTC. Check CISA ↗

How to respond

  1. Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
  2. Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
  3. Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.

Sources and remediation references

This public advisory does not determine whether a particular server is affected. Records are refreshed as sources change; verify urgent decisions against the original advisory.

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