---
id: CVE-2026-76166
title: >-
  Modcluster-core: mod_cluster advertise listener: unauthenticated dos via
  crafted multicast datagram
summary: >-
  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:" …
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cvssSource: cna
cwe:
  - CWE-476
vendor: Red Hat
product: mod_cluster-core
affected:
  - mod_cluster-core
  - jws7-mod_cluster (all versions)
  - jws7-tomcat (all versions)
  - jws7-tomcat-native (all versions)
  - jws7-mod_cluster (all versions)
  - jws7-tomcat (all versions)
  - jws7-tomcat-native (all versions)
  - jws7-mod_cluster (all versions)
  - jws7-tomcat (all versions)
  - jws7-tomcat-native (all versions)
  - mod_cluster-core (all versions)
  - mod_cluster-core (all versions)
  - mod_cluster-core (all versions)
  - mod_cluster-core
  - mod_cluster-core (all versions)
  - mod_cluster-core (all versions)
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-08-20T14:19:26.119248Z'
published: '2026-08-19'
updated: '2026-11-03'
sourceUpdated: '2026-11-03T17:46:20.673Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-76166'
references:
  - url: 'https://access.redhat.com/errata/RHSA-2026:93618'
    label: 'RHSA-2026:93618'
  - url: 'https://access.redhat.com/errata/RHSA-2026:93622'
    label: 'RHSA-2026:93622'
  - url: 'https://access.redhat.com/security/cve/CVE-2026-76166'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2510883'
    label: RHBZ#2510883
tags:
  - cve.org
epss: 0.02718
epssPercentile: 0.86089
ingestedAt: '2026-11-05T20:33:06.329Z'
---

## Overview

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.

## Affected

- `mod_cluster-core`
- `jws7-mod_cluster (all versions)`
- `jws7-tomcat (all versions)`
- `jws7-tomcat-native (all versions)`
- `jws7-mod_cluster (all versions)`
- `jws7-tomcat (all versions)`
- `jws7-tomcat-native (all versions)`
- `jws7-mod_cluster (all versions)`
- `jws7-tomcat (all versions)`
- `jws7-tomcat-native (all versions)`
- `mod_cluster-core (all versions)`
- `mod_cluster-core (all versions)`
- `mod_cluster-core (all versions)`
- `mod_cluster-core`
- `mod_cluster-core (all versions)`
- `mod_cluster-core (all versions)`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

### Workarounds

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.