CVE-2026-12985
Medium
Description
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
SeverityMedium
CVSS6.8
Exploit probability—
Product
Mattermost Server
PublishedSep 14, 2026
First seenSep 14, 2026
Weakness typeCWE-601Open redirect
How to fix
Update
- mattermost mattermost_server11.7.8, 11.8.5, 11.9.1 or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 11.7.0 ≤ v < 11.7.8, 11.8.0 ≤ v < 11.8.5, 11.9.0 ≤ v < 11.9.1 | 11.7.8, 11.8.5, 11.9.1 |
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