CVE-2026-5163

EUVD-2026-30753
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
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
MattermostCNA
6.5 MEDIUM
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: 11%
Affected Products (NVD)
VendorProductVersion
mattermostmattermost_server
11.5.0 ≤
𝑥
< 11.5.2
𝑥
= Vulnerable software versions
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
mattermostmattermost
11.5.0 ≤
𝑥
≤ 11.5.1
CNA
Common Weakness Enumeration
References
https://mattermost.com/security-updates