CVE-2026-5163 — Missing authorization check in AI message rewrite endpoint allows access to private thread content

CVE-2026-5163

Missing authorization check in AI message rewrite endpoint allows access to private thread content PUBLISHED

Description (CNA)

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 (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.5.0 through 11.5.1; unaffected 11.6.0; unaffected 11.5.2

CWE

CWE-862

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.