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CVE-2026-12985Mattermost DCR redirect URI allowlist bypass via improper URL component validation

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

9.3 CRITICALEPSS 0.26%Not in KEVNVD: Analyzed

OverviewAffected ProductsReferences
NVD CVE.org

Overview

Severity

ScoreSeverityVersionVector String
9.3CRITICAL3.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
6.8MEDIUM3.1Mattermost (CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N

Details

CVE ID
CVE-2026-12985
Status
Analyzed
Assigner (CNA)
Mattermost
Published
Sep 14, 2026
Last modified
2026-10-07 17:58 UTC
Weaknesses
  • CWE-601 · URL Redirection to Untrusted Site (“Open Redirect”)

Sources

Refreshed hourly from the sources above. Last fetched 2026-11-08 09:38 UTC.