CVE-2026-5163
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
- CVSS 3.1
- 6.5
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - EPSS
- 0.2% chance of exploitation in the next 30 days; higher than 10% of CVEs (scores of 2026-10-25)
- CWE
- CWE-862
- Published
- Modified
- Record from
- the NVD, synced
Affected
- mattermost:mattermost_server
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-8r89-8w26-cq32 | Go | github.com/mattermost/mattermost/server/v8 | >=11.5.0 <11.5.2 | 11.5.2 |
| GHSA-8r89-8w26-cq32 | Go | github.com/mattermost/mattermost/server/v8 | <8.0.0-20260401090745-f4d1abe7e8f5 | 8.0.0-20260401090745-f4d1abe7e8f5 |
| GHSA-8r89-8w26-cq32 | Go | github.com/mattermost/mattermost-server | <5.3.2-0.20260401090745-f4d1abe7e8f5 | 5.3.2-0.20260401090745-f4d1abe7e8f5 |
| GO-2026-5263 | Go | github.com/mattermost/mattermost-server | >=11.5.0+incompatible <11.5.2+incompatible | 11.5.2+incompatible |
| GO-2026-5263 | Go | github.com/mattermost/mattermost-server/v5 | all versions | no fix published |
| GO-2026-5263 | Go | github.com/mattermost/mattermost-server/v6 | all versions | no fix published |
| GO-2026-5263 | Go | github.com/mattermost/mattermost/server/v8 | <8.0.0-20260401090745-f4d1abe7e8f5 | 8.0.0-20260401090745-f4d1abe7e8f5 |