CVE-2026-12985
Critical
9.3 CVSS v3.1
- Published
- Sep 14, 2026
- Updated
- Oct 7, 2026
- Vendor
- Mattermost
- Affected versions
- See affected products
- Weakness
- CWE-601
Summary
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
Severity
Critical (9.3)CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
Affected products
- Mattermost Mattermost Server >= 11.7.0, < 11.7.8
- Mattermost Mattermost Server >= 11.8.0, < 11.8.5
- Mattermost Mattermost Server >= 11.9.0, < 11.9.1
Exploitation status
Unknown
Technical details
Technical analysis has not been written for this record yet.
Mitigation & remediation
Follow the vendor advisory linked below for patches and workarounds.