CVE-2026-5163

MEDIUM

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

Title source: cna
STIX 2.1

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

References (1)

Core 1
Core References
Vendor Advisory vendor-advisory
MMSA-2026-00645
https://mattermost.com/security-updates

Scores

CVSS v3 6.5
EPSS 0.0021
EPSS Percentile 10.6%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact partial

Details

CWE
CWE-862
Status published
Products (7)
mattermost/mattermost 0 - 8.0.0-20260401090745-f4d1abe7e8f5Go
Mattermost/Mattermost 11.5.0 - 11.5.1
mattermost/mattermost 11.5.0 - 11.5.2Go
Mattermost/Mattermost 11.5.2
Mattermost/Mattermost 11.6.0
mattermost/mattermost-server 0 - 5.3.2-0.20260401090745-f4d1abe7e8f5Go
mattermost/mattermost_server 11.5.0 - 11.5.2
Published May 18, 2026
Tracked Since May 18, 2026