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

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-04 · updated 2026-10-21
Weakness: CWE-122

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.

Affected products

Red Hat OpenShift Container Platform 4.18: all versions
Red Hat Enterprise Linux 10: all versions — fixed in 0:3.1.10-1.el10_2.2
Red Hat Enterprise Linux 10.0 Extended Update Support: all versions — fixed in 0:3.1.9-1.el10_0.3
Red Hat Enterprise Linux 7 Extended Lifecycle Support: all versions — fixed in 0:2.4.5-7.el7_9.4
Red Hat Enterprise Linux 8: all versions — fixed in 0:3.1.8-1.el8_10.2
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: all versions — fixed in 0:3.1.0-3.el8_4.3
Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: all versions — fixed in 0:3.1.0-3.el8_4.3
Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support: all versions — fixed in 0:3.1.5-2.el8_6.2
Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On: all versions — fixed in 0:3.1.5-2.el8_6.2
Red Hat Enterprise Linux 8.8 Telecommunications Update Service: all versions — fixed in 0:3.1.7-1.el8_8.2
Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions: all versions — fixed in 0:3.1.7-1.el8_8.2
Red Hat Enterprise Linux 9: all versions — fixed in 0:3.1.10-1.el9_8.2
Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions: all versions — fixed in 0:3.1.7-1.el9_2.2
Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions: all versions — fixed in 0:3.1.8-1.el9_4.2
Red Hat Enterprise Linux 9.6 Extended Update Support: all versions — fixed in 0:3.1.9-2.el9_6.2

How to fix

Upgrade to a fixed version: Red Hat Enterprise Linux 10 0:3.1.10-1.el10_2.2; Red Hat Enterprise Linux 10.0 Extended Update Support 0:3.1.9-1.el10_0.3; Red Hat Enterprise Linux 7 Extended Lifecycle Support 0:2.4.5-7.el7_9.4; Red Hat Enterprise Linux 8 0:3.1.8-1.el8_10.2; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 0:3.1.0-3.el8_4.3; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 0:3.1.0-3.el8_4.3; Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support 0:3.1.5-2.el8_6.2; Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On 0:3.1.5-2.el8_6.2; Red Hat Enterprise Linux 8.8 Telecommunications Update Service 0:3.1.7-1.el8_8.2; Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions 0:3.1.7-1.el8_8.2; Red Hat Enterprise Linux 9 0:3.1.10-1.el9_8.2; Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions 0:3.1.7-1.el9_2.2. Check the vendor advisory for mitigations.

References

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