CVE-2026-4055: Insufficient permission validation on cross-team playbook run creation

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-21 · updated 2026-07-23
Weakness: CWE-863

Description

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

Affected products

Mattermost: from 10.11.0 before 10.11.17; from 11.5.0 before 11.5.5; from 11.6.0 before 11.6.2 — fixed in 10.11.17, 11.5.5, 11.6.2

How to fix

Upgrade to a fixed version: Mattermost 10.11.17, 11.5.5, 11.6.2. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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