Mattermost 11.5.x <= 11.5.1 Playbook Run Create Auth Bypass
CVE-2026-4055 Published on May 21, 2026
Insufficient permission validation on cross-team playbook run creation
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
Vulnerability Analysis
CVE-2026-4055 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
What is an AuthZ Vulnerability?
The software performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
CVE-2026-4055 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-4055
Want to know whenever a new CVE is published for MatterMost? stack.watch will email you.
Affected Versions
Mattermost:- Version 11.5.0, <= 11.5.1 is affected.
- Version 11.6.0 is unaffected.
- Version 11.5.2 is unaffected.
- Version 10.11.14 is unaffected.
- Version 11.4.4 is unaffected.