CVE-2026-26304 Permission Bypass in Playbook Run Creation

What is CVE-2026-26304?

CVE-2026-26304 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 16 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2 fail to verify run_create permission for empty playbookId, which allows team members to create unauthorized runs via the playbook run API. Mattermost Advisory ID: MMSA-2025-00542

Weakness: CWE-863

Which versions are affected by CVE-2026-26304?

3 open source packages ship an affected version, including github.com/mattermost/mattermost-plugin-playbooks. It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2026-26304?

Upgrade github.com/mattermost/mattermost-plugin-playbooks to 1.41.1-0.20260316224925-705f54a81841 or later.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

Is CVE-2026-26304 being exploited?

There is no known exploitation of CVE-2026-26304 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost Server

• CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers Critical 9.9
• CVE-2025-12421 Account Takeover via Code Exchange Endpoint Critical 9.9
• CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User Critical 9.9
• CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards Critical 9.9
• CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive Critical 9.9

All Mattermost Mattermost Server vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-4pmx-622h-x359, GO-2026-4812.