# CVE-2026-81665: Corosync heap-based buffer overflow in Totem message reassembly

Source: https://junglewise.ai/threats/cve-2026-81665-corosync-heap-based-buffer-overflow-in-totem-message-reassembly  
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-2026-81665 · Severity: high · CVSS 7.5 · Published 2026-09-04

Corosync is cluster management software that enables multiple servers to communicate and coordinate as a unified system. A heap buffer overflow vulnerability in its message reassembly logic allows an attacker on the same network segment to send specially crafted cluster messages that can crash the Corosync daemon, disrupting cluster operations and potentially compromising the entire cluster infrastructure.

Technologies: [Corosync](https://junglewise.ai/threats/technologies/corosync). Vendors: [Corosync](https://junglewise.ai/threats/vendors/corosync).

## Quick answers

**Is CVE-2026-81665 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-81665 being exploited in the wild.

**How severe is CVE-2026-81665?** High severity, with a CVSS score of 7.5, published 4 September 2026.

**Which products and versions are affected?** Corosync <UNKNOWN.

**Is there a fix for CVE-2026-81665?** 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-2026-81665 attacked?** It is attacked from the adjacent network or over the network.

**Am I affected by CVE-2026-81665?** Check whether you run Corosync 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

A heap-based buffer overflow exists in Corosync's Totem Process Group (totempg) message reassembly component. When processing fragmented multicast messages, the reassembly buffer lacks proper runtime bounds checking in release builds, allowing an attacker with network adjacency to send crafted multicast protocol messages that overflow the buffer with attacker-controlled data. This can cause the Corosync daemon to crash (denial of service), and with sufficient control over heap corruption, may enable further arbitrary code execution. A patch is available via Red Hat security update RHSA-2026:67872.

## Affected products

- Corosync Corosync <UNKNOWN

## Timeline

- 2026-09-04: disclosed
- 2026-09-16: advisory: Red Hat RHSA-2026:67872 issued

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/errata/RHSA-2026:67872](https://access.redhat.com/errata/RHSA-2026:67872)

## Related threats

- [Corosync integer overflow in membership commit token handling](https://junglewise.ai/threats/cve-2026-81666-corosync-integer-overflow-in-membership-commit-token-handling)
- [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)