CVE-2026-16453

EUVD-2026-102745
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to verify the integrity of the SAML RelayState POST parameter which allows an authenticated SAML user to join any team, including invite-only teams, via forging the team_id or invite_id fields in the RelayState.. Mattermost Advisory ID: MMSA-2026-00727
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
MattermostCNA
7.1 HIGH
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: 7.82%
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
mattermostmattermost
𝑥
≤ 11.10.0
CNA
mattermostmattermost
11.7.0 ≤
𝑥
≤ 11.7.9
CNA
mattermostmattermost
11.9.0 ≤
𝑥
≤ 11.9.1
CNA
mattermostmattermost
11.8.0 ≤
𝑥
≤ 11.8.5
CNA
Common Weakness Enumeration
References
https://mattermost.com/security-updates