CVE-2026-8821
Received Received - Intake

Mattermost Permission Bypass in Playbook Run Creation

Publication date: 2026-09-14

Last updated on: 2026-09-14

Assigner: Mattermost, Inc.

Description
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

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Meta Information

Published
2026-09-14
Last Modified
2026-09-14
Generated
2026-09-14
AI Q&A
2026-09-14
EPSS Evaluated
N/A
NVD
CVE-2026-8821
EUVD
EUVD-2026-77371

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
mattermost mattermost to 11.9.0 (inc)
mattermost mattermost to 11.8.4 (inc)
mattermost mattermost to 11.7.7 (inc)
mattermost mattermost to 10.11.22 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-862 The product does not perform an authorization check when an actor attempts to access a resource or perform an action.

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Executive Summary

Mattermost versions between 11.9.0 and older, 11.8.4 and older, 11.7.7 and older, and 10.11.22 and older have a flaw where channel member-management permissions are not properly checked during playbook run creation. This allows an authenticated user who is a channel member to add any other user to a restricted channel by manipulating the run owner field.

Impact Analysis

An attacker with basic access could escalate privileges by adding unauthorized users to private channels, potentially accessing sensitive information or disrupting operations. This could lead to data breaches or unauthorized modifications within restricted channels.

Compliance Impact

This vulnerability could violate compliance requirements that mandate strict access controls for sensitive data, such as GDPR's data protection principles or HIPAA's access controls for protected health information. Unauthorized access to restricted channels may lead to regulatory penalties.

Mitigation Strategies

Update Mattermost to a version that fixes the permission validation issue. Specifically, upgrade to versions beyond 11.9.0, 11.8.4, 11.7.7, or 10.11.22 depending on your current installation.

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