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

High 7.5 Published 4 Sep 2026 Updated 21 Oct 2026

A heap-based buffer overflow in Corosync allows network-adjacent attackers to crash the cluster daemon or potentially execute code via crafted multicast messages.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-81665?

CVE-2026-81665 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 4 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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.

Weakness: CWE-122

Which versions are affected by CVE-2026-81665?

Linux distribution packages (40)

`corosync` AlmaLinux:10	All versions	`3.1.10-1.el10_2.2`
`corosync-vqsim` AlmaLinux:10	All versions	`3.1.10-1.el10_2.2`
`corosynclib` AlmaLinux:10	All versions	`3.1.10-1.el10_2.2`
`corosynclib-devel` AlmaLinux:10	All versions	`3.1.10-1.el10_2.2`
`corosync` AlmaLinux:8	All versions	`3.1.8-1.el8_10.2`
`corosync-vqsim` AlmaLinux:8	All versions	`3.1.8-1.el8_10.2`
`corosynclib` AlmaLinux:8	All versions	`3.1.8-1.el8_10.2`
`corosynclib-devel` AlmaLinux:8	All versions	`3.1.8-1.el8_10.2`
`spausedd` AlmaLinux:8	All versions	`3.1.8-1.el8_10.2`
`corosync` AlmaLinux:9	All versions	`3.1.10-1.el9_8.2`
`corosync-vqsim` AlmaLinux:9	All versions	`3.1.10-1.el9_8.2`
`corosynclib` AlmaLinux:9	All versions	`3.1.10-1.el9_8.2`
`corosynclib-devel` AlmaLinux:9	All versions	`3.1.10-1.el9_8.2`
`corosync` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosync-debuginfo` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosync-debugsource` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosync-vqsim` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosync-vqsim-debuginfo` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosynclib` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosynclib-debuginfo` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosynclib-devel` Red Hat:enterprise_linux:10.2	All versions	`0:3.1.10-1.el10_2.2`
`corosync` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`corosync-debuginfo` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`corosync-qdevice` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`corosync-qnetd` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`corosynclib` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`corosynclib-devel` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`spausedd` Red Hat:enterprise_linux:7::server	All versions	`0:2.4.5-7.el7_9.4`
`corosync` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`corosync-debuginfo` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`corosync-debugsource` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`corosync-vqsim-debuginfo` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`corosynclib` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`corosynclib-debuginfo` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`spausedd-debuginfo` Red Hat:enterprise_linux:8::appstream	All versions	`0:3.1.8-1.el8_10.2`
`corosync-debuginfo` Red Hat:enterprise_linux:8::crb	All versions	`0:3.1.8-1.el8_10.2`
`corosync-debugsource` Red Hat:enterprise_linux:8::crb	All versions	`0:3.1.8-1.el8_10.2`
`corosync-vqsim` Red Hat:enterprise_linux:8::crb	All versions	`0:3.1.8-1.el8_10.2`
`corosync-vqsim-debuginfo` Red Hat:enterprise_linux:8::crb	All versions	`0:3.1.8-1.el8_10.2`
`corosynclib-debuginfo` Red Hat:enterprise_linux:8::crb	All versions	`0:3.1.8-1.el8_10.2`

How do I fix CVE-2026-81665?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-81665 being exploited?

There is no known exploitation of CVE-2026-81665 in the wild and no public exploit code.

Sources

Also known as ALSA-2026:67872, ALSA-2026:67873, ALSA-2026:69277, AZL-99888, CLSA-2026-1790008457, CLSA-2026-1790352190 and 18 more.