Bypass channel memberperm in Mattermost 11.9.x10.11.22 CVE20268821
CVE-2026-8821 Published on September 14, 2026
Playbooks run owner channel membership permission bypass
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate channel member-management permission during playbook run creation, allowing an authenticated channel member to add an arbitrary user to a restricted channel via the run owner field.. Mattermost Advisory ID: MMSA-2026-00677
Vulnerability Analysis
CVE-2026-8821 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 a high impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
What is an AuthZ Vulnerability?
The software does not perform an authorization check when an actor attempts to access a resource or perform an action.
CVE-2026-8821 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-8821
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Affected Versions
Mattermost:- Version 11.9.0, <= 11.9.0 is affected.
- Version 11.8.0, <= 11.8.4 is affected.
- Version 11.7.0, <= 11.7.7 is affected.
- Version 10.11.0, <= 10.11.22 is affected.
- Version 11.10.0 is unaffected.
- Version 11.9.1 is unaffected.
- Version 11.8.5 is unaffected.
- Version 11.7.8 is unaffected.
- Version 10.11.23 is unaffected.