CVE-2026-16453

High

Description

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

SeverityHigh

CVSS7.1

Exploit probability—

Product

Mattermost Server

PublishedOct 16, 2026

First seenOct 16, 2026

Weakness typeCWE-472CWE-472

How to fix

Update

mattermost mattermost_server11.7.10, 11.8.6, 11.9.2 or later

Vendor advisories

mattermost.com/security-updates

Affected products

Product	Affected versions	Fixed in
mattermost mattermost_server	11.7.0 ≤ v < 11.7.10, 11.8.0 ≤ v < 11.8.6, 11.9.0 ≤ v < 11.9.2, 11.10.0	11.7.10, 11.8.6, 11.9.2

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