CVE-2026-12985
Published:September 14, 2026
Updated:September 22, 2026
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 Mattermost failed to validate Dynamic Client Registration redirect URIs by URL component (matching glob patterns against the raw URI string instead) which allows a remote unauthenticated attacker to register an OAuth client with an attacker-controlled callback host that bypasses the configured redirect URI allowlist via a crafted redirect URI that places an allowlisted host/path suffix inside the query string.. Mattermost Advisory ID: MMSA-2026-00700
Affected Packages
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v11.8.0 <v11.8.5Fix Suggestion:
Update to version v11.8.5https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v11.7.0 <v11.7.8Fix Suggestion:
Update to version v11.7.8https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) =v11.9.0 <v11.9.1Fix Suggestion:
Update to version v11.9.1github.com/mattermost/mattermost/server/public (GO):
Affected version(s) >=v0.2.1 <v0.4.4Fix Suggestion:
Update to version v0.4.4Related Resources (1)
Do you need more information?
Contact UsCVSS v4
Base Score:
7.6
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
6.8
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
NONE
Weakness Type (CWE)
URL Redirection to Untrusted Site ('Open Redirect')
EPSS
Base Score:
0.28