Bug 2510883 (CVE-2026-76166)

Summary:	CVE-2026-76166 modcluster-core: mod_cluster Advertise Listener: unauthenticated DoS via crafted multicast datagram
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	anujha, aschwart, asoldano, aszczucz, bbaranow, bmaxwell, boliveir, bstansbe, csutherl, dlofthou, drichtar, dsoumis, istudens, ivassile, iweiss, jclere, jwon, mosmerov, mposolda, msvehla, nwallace, pberan, pesilva, pjindal, plodge, pmackay, rmartinc, rmaucher, rstancel, ssilvert, sthorger, szappis, thjenkin, vdosoudi, vmuzikar
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
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Fixed In Version:		Doc Type:	---
Doc Text:	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.	Story Points:	---
Clone Of:		Environment:
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-08-04 04:37:34 UTC

Reported via PSIRTSUPT-20286 by Ta Duc Thien from Ninh Thanh Cyber Security (NTCS).

Vulnerability in org.jboss.modcluster core module, class AdvertiseListenerImpl. A crafted UDP multicast datagram (missing Date/Digest/Sequence headers) triggers an uncaught NullPointerException in verifyDigest() that kills the advertise worker thread permanently. Works even with AdvertiseSecurityKey configured (NPE fires before key comparison). Silent failure — isListening() keeps returning true.

Upstream: https://github.com/modcluster/mod_cluster
Affected version: 2.1.0.Final (confirmed by reporter, same code on current main branch)
Reporter's PoC and full write-up attached to PSIRTSUPT-20286.