CVE-2026-5163 | THREATINT

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

PUBLISHED Reserved 2026-03-30 | Published 2026-05-18 | Updated 2026-05-18 | Assigner Mattermost

MEDIUM: 6.5CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Problem types

CWE-862: Missing Authorization

Product status

Default status

unaffected

11.5.0 (semver)

affected

11.6.0

unaffected

11.5.2

unaffected

Credits

daw10 finder

References

mattermost.com/security-updates (MMSA-2026-00645) vendor-advisory

cve.org (CVE-2026-5163)

nvd.nist.gov (CVE-2026-5163)

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