CVE-2026-5163

medium

Published 2026-05-18 · Modified 2026-05-18

CVSS v3

6.5

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

CVSS v2

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VIR risk

6.5

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

Predictions

Exploit likelihood

75%

Patch ETA

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Heuristic predictions, AS-IS, for prioritization only.

Mitigations

vendor Authored 2026-05-27

Vendor advisory: responsibledisclosure@mattermost.com — https://mattermost.com/security-updates

Application impact

Vendor	Product	Versions	Fixed
mattermost	mattermost_server	`{"startIncluding":"11.5.0","endExcluding":"11.5.2"}`	`11.5.2`

References

https://mattermost.com/security-updates

CWEs

CWE-862

Verify integrity in audit chain (admin only). AS-IS.