CVE-2026-81665

Corosync: corosync: heap-based buffer overflow in totempg assembly buffer during fragmented message reassembly

publishedCWE-122

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.

Technical severity7.5 highCVSS 3.1 · CNA: redhat

Published2026-09-04Source updated 2026-11-02

Collected2026-11-022 attributed sources

Fixes and workarounds

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.

Source: CNA: redhat

Affected products and versions

Affected products, source version ranges and reporting authorities
Product	Versions	Authority
Red Hat Enterprise Linux 10 Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.10-1.el10_2.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 10.0 Extended Update Support Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.9-1.el10_0.3; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 7 Extended Lifecycle Support Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:2.4.5-7.el7_9.4; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8 Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.8-1.el8_10.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.0-3.el8_4.3; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.0-3.el8_4.3; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.5-2.el8_6.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.5-2.el8_6.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8.8 Telecommunications Update Service Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.7-1.el8_8.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.7-1.el8_8.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 9 Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.10-1.el9_8.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.7-1.el9_2.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.8-1.el9_4.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 9.6 Extended Update Support Red Hat `corosync` https://access.redhat.com/downloads/content/package-browser/	≥ 0:3.1.9-2.el9_6.2; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat OpenShift Container Platform 4 Red Hat `openshift/ose-rhel-coreos-9` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat
Red Hat OpenShift Container Platform 4 Red Hat `rhcos` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat
Red Hat OpenShift Container Platform 5 Red Hat `openshift/ose-rhel-coreos-9` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat
Red Hat OpenShift Container Platform 5 Red Hat `rhcos` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat

Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.

CVSS assessments

CVSS scores, vectors and reporting authorities
Version / score	Vector	Authority
3.1 / 7.5 high	`CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`	CNA: redhat

Exploit evidence

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

References

https://access.redhat.com/errata/RHSA-2026:67872CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:67873CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:67878CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:67879CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:67880CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:67881CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:68574CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:69277CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:69278CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:69279CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:69280CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/security/cve/CVE-2026-81665CNA: redhat · vdb-entry, x_refsource_REDHAT
https://bugzilla.redhat.com/show_bug.cgi?id=2524910CNA: redhat · issue-tracking, x_refsource_REDHAT

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