CVE-2026-5163CWE-862broken-access-control

CVE-2026-5163

Medium · published May 18, 2026

CVSS v3.1
6.5
EPSS
0%
Percentile
26.3
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
6.5 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00340 · 26.3th percentile
Weakness
CWE-862 · Missing Authorization
Published
2026-05-18T13:16Z
Affected products (1)
ProductVersionsFixed in
mattermost/mattermost_server≥ 11.5.0, < 11.5.211.5.2
References (1)
https://mattermost.com/security-updates · [email protected]
EPSS history
Timeline
  • 18 MAY 08:11Z
    Missing authorization check in AI message rewrite endpoint allows access to private thread content
    cvelistv5