Corosync: corosync: heap-based buffer overflow in totempg assembly buffer during fragmented message reassembly (CVE-2026-81665)

Why this deserves its current priority

CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Red Hat/openshift/ose-rhel-coreos-9 (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Red Hat/openshift/ose-rhel-coreos-9generic	*	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Red Hat/openshift/ose-rhel-coreos-9.
Review the reported fix. Source-reported workaround: There is no complete mitigation for this vulnerability short of a fix, but the following steps significantly reduce risk: 1. Ensure cluster message authentication is enabled in corosync.conf: set crypto_cipher to aes256 and crypto_hash to sha256 (or stronger) in the totem {} block, with a shared key generated by corosync-keygen. This is the default when clusters are configured via 'pcs cluster setup', and disabling it (cipher=none/hash=none) is an explicitly unsupported configuration per upstream maintainer guidance. 2. Restrict network access to the cluster communication ports (default 5405-5412/UDP) to trusted cluster node addresses only, using firewalld or other firewall rules. 3. Ensure SELinux is running in enforcing mode on cluster nodes to limit the impact of any successful exploitation.

Evidence timeline and material changes

Published upstream
Sep 4, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 30, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 4, 2026

Sources and claim methodology

Upstream source description

A heap-based buffer overflow was found in Corosync's Totem Process Group (totempg) message reassembly. When processing fragmented multicast messages, the buffer used to reassemble fragments lacks a runtime bounds check in release builds. A network-adjacent attacker able to send crafted multicast protocol messages to the cluster could cause a heap buffer overflow with attacker-controlled data. This can crash the Corosync daemon, causing a denial of service to the entire cluster, and may potentially allow further exploitation given sufficient heap-corruption control.

Quoted source text, attributed separately from HOL analysis.

Corosync: corosync: heap-based buffer overflow in totempg assembly buffer during fragmented message reassemblyCVE-2026-81665