Is CVE-2026-18560 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-18560 being exploited in the wild.

How severe is CVE-2026-18560?

Medium severity, with a CVSS score of 4.3, published 16 October 2026.

Which products and versions are affected?

Mattermost Server 11.10.x through 11.10.0, 11.7.x through 11.7.9, 11.9.x through 11.9.1, 11.8.x through 11.8.5.

Is there a fix for CVE-2026-18560?

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-2026-18560 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-18560?

Check whether you run Mattermost Server 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-2026-18560: Mattermost authorization bypass in post flag status

CVE-2026-18560 · Severity: medium · CVSS 4.3 · Published 2026-10-16

Mattermost is a team communication and collaboration platform. In affected versions, users without content-review permissions can discover whether posts have been flagged for moderation by making direct API calls, bypassing the intended access restrictions. This information leakage could allow unauthorized users to monitor moderation actions on the platform.

Technologies: Mattermost Server. Vendors: Mattermost.

Quick answers

Is CVE-2026-18560 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-18560 being exploited in the wild.
How severe is CVE-2026-18560?: Medium severity, with a CVSS score of 4.3, published 16 October 2026.
Which products and versions are affected?: Mattermost Server 11.10.x through 11.10.0, 11.7.x through 11.7.9, 11.9.x through 11.9.1, 11.8.x through 11.8.5.
Is there a fix for CVE-2026-18560?: 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-2026-18560 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-18560?: Check whether you run Mattermost Server 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

The vulnerability is an authorization bypass (CWE-639) where Mattermost fails to validate user permissions before processing API requests related to flagged post status. An unauthenticated attacker or low-privileged user can call the API directly to infer flagged status of posts, achieving information disclosure. A fix is available in patched versions.

Affected products

Mattermost Mattermost Server 11.10.x through 11.10.0, 11.7.x through 11.7.9, 11.9.x through 11.9.1, 11.8.x through 11.8.5

Timeline

2026-10-16: disclosed

References

https://mattermost.com/security-updates

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