CVE-2026-5163
MEDIUM6.5EPSS 0.04%Mattermost doesn't verify channel membership when processing AI-assisted message rewrites
Published: 5/18/2026Modified: 6/1/2026
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
Affected packages (2)
- Go/github.com/mattermost/mattermost-serverfrom 0, < 5.3.2-0.20260401090745-f4d1abe7e8f5
- Go/github.com/mattermost/mattermost/server/v8>= 11.5.0, < 11.5.2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N |