# CVE-2026-76166: Modcluster-core: mod_cluster advertise listener: unauthenticated dos via crafted multicast datagram

Status: published. Published: 2026-08-19. Updated: 2026-11-03.

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.

## Remediation

- workaround: Disable multicast-based proxy advertisement and use static proxy configuration instead. When advertisement must be enabled, ensure the multicast network segment (default 224.0.1.105:23364) is properly isolated and not accessible from untrusted network segments. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat JBoss Web Server 7.0.3 (mod_cluster-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 10 (jws7-mod_cluster): ≥ 0:2.1.1-1.Final_redhat_00001.1.el10jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 10 (jws7-tomcat): ≥ 0:11.0.21-10.redhat_00010.1.el10jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 10 (jws7-tomcat-native): ≥ 0:1.3.7-4.redhat_4.el10jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 8 (jws7-mod_cluster): ≥ 0:2.1.1-1.Final_redhat_00001.1.el8jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 8 (jws7-tomcat): ≥ 0:11.0.21-10.redhat_00010.1.el8jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 8 (jws7-tomcat-native): ≥ 0:1.3.7-4.redhat_4.el8jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 9 (jws7-mod_cluster): ≥ 0:2.1.1-1.Final_redhat_00001.1.el9jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 9 (jws7-tomcat): ≥ 0:11.0.21-10.redhat_00010.1.el9jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 7.0 on RHEL 9 (jws7-tomcat-native): ≥ 0:1.3.7-4.redhat_4.el9jws; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 7 (mod_cluster-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8 (mod_cluster-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform Expansion Pack (mod_cluster-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 5 (mod_cluster-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Web Server 6 (mod_cluster-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Single Sign-On 7 (mod_cluster-core): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 4.3 (medium); CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 1.03% as of 2026-11-03; percentile 63.89%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-476

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2026:93618 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:93622 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-76166 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2510883 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-76166; retrieved 2026-11-03; source updated 2026-11-03

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-76166; retrieved 2026-11-03; source updated Not reported

Revision: ff0a05caf6ab308146cb2864cc13fde3d94b23e85f0e0497c8ddc88c5cbeab8d

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