CVE-2026-5163
Missing authorization check in AI message rewrite endpoint allows access to private thread content
- State
- Published
- Severity
- 6.5 Medium
- Published
- May 18, 2026
- Updated
- May 18, 2026
- Reserved
- Mar 30, 2026
Description
Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 6.5 Medium | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N | Mattermost |
Weaknesses
- CWE-862 Missing Authorization
Affected Products
| Product | Versions |
|---|---|
MattermostMattermost |
|
References
- MMSA-2026-00645vendor-advisory
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