CVSS 9.3 (critical) · published 2026-09-14
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 products (NVD): mattermost mattermost_server
Fixed in (NVD): 11.7.8, 11.8.5, 11.9.1
Weakness: CWE-601
Source: NVD CVE-2026-12985
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