CVE-2026-5163GO-2026-5263GHSA-8R89-8W26-CQ32
Missing authorization check in AI message rewrite endpoint allows access to private thread content
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 11.5.2+incompatible, 8.0.0-20260401090745-f4d1abe7e8f5, 11.5.2, 5.3.2-0.20260401090745-f4d1abe7e8f5
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
CISA's decision points: whether it is exploited, whether attacks can be automated, and how much control an attacker gets. Assessed (SSVC 2.0.3).What do these mean? →
- Exploitation: none
- Automatable: no
- Technical impact: partial
Summary
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
Timeline
- CVE published
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: partial
- Record last updated
Affected versions
- Mattermost Mattermost
From 11.5.0 · through 11.5.1
- github.com/mattermost/mattermost-serverGo
From 11.5.0+incompatible · fixed in 11.5.2+incompatible
- github.com/mattermost/mattermost-server/v5Go
All versions
- github.com/mattermost/mattermost-server/v6Go
All versions
- github.com/mattermost/mattermost/server/v8Go
fixed in 8.0.0-20260401090745-f4d1abe7e8f5
- github.com/mattermost/mattermost/server/v8Go
From 11.5.0 · fixed in 11.5.2
- github.com/mattermost/mattermost-serverGo
fixed in 5.3.2-0.20260401090745-f4d1abe7e8f5