# CVE-2026-81666: Corosync integer overflow in membership commit token handling

Source: https://junglewise.ai/threats/cve-2026-81666-corosync-integer-overflow-in-membership-commit-token-handling  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-04. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-81666 · Severity: medium · CVSS 6.5 · Published 2026-09-04

Corosync is cluster management software used to coordinate High Availability deployments across multiple servers. An integer overflow vulnerability in the message length validation on 32-bit systems allows a malicious network packet to crash the Corosync daemon, causing the affected cluster node to become unavailable. While 64-bit systems are unaffected, this can disrupt cluster operations for affected 32-bit deployments.

Technologies: [Corosync](https://junglewise.ai/threats/technologies/corosync). Vendors: [Corosync](https://junglewise.ai/threats/vendors/corosync), [Red Hat](https://junglewise.ai/threats/vendors/red-hat).

## Quick answers

**Is CVE-2026-81666 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81666 being exploited in the wild.

**How severe is CVE-2026-81666?** Medium severity, with a CVSS score of 6.5, published 4 September 2026.

**Which products and versions are affected?** Corosync unspecified; Red Hat Enterprise Linux High Availability Add-On 7 through 10.

**Is there a fix for CVE-2026-81666?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-81666 attacked?** It is attacked from the adjacent network.

**Am I affected by CVE-2026-81666?** Check whether you run Corosync or Red Hat Enterprise Linux High Availability Add-On at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An integer overflow in the check_memb_commit_token_sanity function bypasses length validation for membership commit token messages on 32-bit systems. The vulnerability arises from a 32-bit integer multiplication in the message length calculation that overflows, allowing an attacker to craft a network packet that passes validation but triggers an out-of-bounds memory access. The attack is network-adjacent (requires access to cluster communication network, typically UDP ports 5405-5412) and requires no authentication. The overflow does not occur on 64-bit systems due to C integer-promotion rules that cause the calculation to be evaluated in 64-bit arithmetic. Clusters with message authentication enabled (the default in Red Hat's HA configuration) have significantly reduced risk. A patch is expected from upstream Corosync.

## Affected products

- Red Hat Enterprise Linux High Availability Add-On 7 through 10
- Corosync Corosync unspecified

## Timeline

- 2026-09-04: disclosed

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-81666](https://access.redhat.com/security/cve/CVE-2026-81666)

## Related threats

- [Corosync heap-based buffer overflow in Totem message reassembly](https://junglewise.ai/threats/cve-2026-81665-corosync-heap-based-buffer-overflow-in-totem-message-reassembly)
- [Corosync integer overflow in join message validation](https://junglewise.ai/threats/cve-2026-35092-corosync-integer-overflow-in-join-message-validation)
- [Corosync Cluster Engine out-of-bounds read in membership commit token check](https://junglewise.ai/threats/cve-2026-35091-corosync-cluster-engine-out-of-bounds-read-in-membership-commit)