CVE-2026-4055: Mattermost has an Incorrect Authorization issue

May 21, 2026 (updated June 23, 2026)

Mattermost versions 11.5.x <= 11.5.1 fail to validate team-level run_create permission against the target team when creating a playbook run which allows an authenticated team member to create runs in teams where they lack permission via specifying a different team ID in the run creation API request. Mattermost Advisory ID: MMSA-2026-00629.

References

github.com/advisories/GHSA-6cfr-wp44-6qmv
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-4055

Code Behaviors & Features

Detect and mitigate CVE-2026-4055 with GitLab Dependency Scanning

Secure your software supply chain by verifying that all open source dependencies used in your projects contain no disclosed vulnerabilities. Learn more about Dependency Scanning →