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.

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

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. Vendors: Corosync, 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

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