Quick answers
- Is CVE-2026-18256 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-18256 being exploited in the wild.
- How severe is CVE-2026-18256?
- Medium severity, with a CVSS score of 4.3, published 16 October 2026.
- Which products and versions are affected?
- Mattermost Server 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.8.x <= 11.8.5, 11.9.x <= 11.9.1.
- Is there a fix for CVE-2026-18256?
- 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-2026-18256 attacked?
- It is attacked over the network, in a web application.
- Am I affected by CVE-2026-18256?
- 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
Mattermost fails to properly enforce access controls on the team search API endpoint, allowing authenticated users to enumerate private teams via modified search requests. The vulnerability affects versions 11.10.x through 11.10.0, 11.7.x through 11.7.9, 11.8.x through 11.8.5, and 11.9.x through 11.9.1. An authenticated attacker can extract metadata (ID, name, display name) about private teams without proper authorization, classified as an information disclosure vulnerability with network attack vector requiring valid authentication.
Affected products
- Mattermost Mattermost Server 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.8.x <= 11.8.5, 11.9.x <= 11.9.1
Timeline
- 2026-10-16: disclosed