GHSA-8r89-8w26-cq32
Mattermost doesn't verify channel membership when processing AI-assisted message rewrites
Packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| Go | github.com/mattermost/mattermost/server/v8 | >= 11.5.0, < 11.5.2 | 11.5.2 |
| Go | github.com/mattermost/mattermost/server/v8 | < 8.0.0-20260401090745-f4d1abe7e8f5 | 8.0.0-20260401090745-f4d1abe7e8f5 |
| Go | github.com/mattermost/mattermost-server | < 5.3.2-0.20260401090745-f4d1abe7e8f5 | 5.3.2-0.20260401090745-f4d1abe7e8f5 |
Details
As written in the advisory (Markdown source, shown as plain text).
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
References
External links from the advisory. They lead to third-party sites.