Vulnerability · Published Sep 14, 2026 · Assigned by Mattermost
CVE-2026-8821Playbooks run owner channel membership permission bypass
High 7.1
In plain English
A high-severity missing authorization in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 22% of all known vulnerabilities).
Severity (CVSS 3.1)7.1High
Exploit odds (30 days)0.3%top 78.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Mattermost | Mattermost | 11.9.0 – through 11.9.011.8.0 – through 11.8.411.7.0 – through 11.7.710.11.0 – through 10.11.22 |
Weakness: CWE-862 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
References
- MMSA-2026-00677 vendor-advisory