Medium severity6.5NVD Advisory· Published May 18, 2026· Updated May 18, 2026
CVE-2026-5163
CVE-2026-5163
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
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
github.com/mattermost/mattermost/server/v8Go | >= 11.5.0, < 11.5.2 | 11.5.2 |
github.com/mattermost/mattermost/server/v8Go | < 8.0.0-20260401090745-f4d1abe7e8f5 | 8.0.0-20260401090745-f4d1abe7e8f5 |
github.com/mattermost/mattermost-serverGo | < 5.3.2-0.20260401090745-f4d1abe7e8f5 | 5.3.2-0.20260401090745-f4d1abe7e8f5 |
Affected products
4cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*range: >=11.5.0,<11.5.2
- (no CPE)range: <=11.5.1
- ghsa-coords2 versionspkg:golang/github.com/mattermost/mattermost-serverpkg:golang/github.com/mattermost/mattermost/server/v8
< 5.3.2-0.20260401090745-f4d1abe7e8f5+ 1 more
- (no CPE)range: < 5.3.2-0.20260401090745-f4d1abe7e8f5
- (no CPE)range: >= 11.5.0, < 11.5.2
Patches
Vulnerability mechanics
References
4- github.com/advisories/GHSA-8r89-8w26-cq32ghsaADVISORY
- mattermost.com/security-updatesnvdVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2026-5163ghsaADVISORY
- github.com/mattermost/mattermost/commit/f4d1abe7e8f545f1a87f463fa9fe451c731aebf8ghsaWEB
News mentions
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