CVE-2026-5163 MEDIUM

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

Vendor Mattermost
Product Mattermost
Weakness CWE-862 · Missing authorization
Published May 18, 2026
Last update May 18, 2026
View on NVD All CVEs

CVSS base score

6.5/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Confidentiality High
Integrity None

CVSS vector

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

What the vulnerability does

01Description

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

Key dates

02Disclosure timeline

May 18, 2026 CVE published
May 18, 2026 Record updated