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TI-2026-11047 Aliases CVE-2026-12985GHSA-c92j-r2f4-67xg

Mattermost DCR redirect URI allowlist bypass via improper URL component validation

Priority MEDIUM 42CWE-601Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
Spoofing
Confidentiality · integrity · availability
High · High · None
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from 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

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00268 18th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.10.0, 11.9.1, 11.8.5 +1

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MattermostMattermost11.9.0 – 11.9.0; 11.8.0 – 11.8.4; 11.7.0 – 11.7.711.10.0, 11.9.1, 11.8.5, 11.7.8Patch availableCNA
  • Mattermost VendorMattermost Affected 11.9.0 – 11.9.0; 11.8.0 – 11.8.4; 11.7.0 – 11.7.7 Fixed in 11.10.0, 11.9.1, 11.8.5, 11.7.8 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*11.7.0 to before 11.7.8; 11.8.0 to before 11.8.5; 11.9.0 to before 11.9.1VulnerableMattermost
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 11.7.0 to before 11.7.8; 11.8.0 to before 11.8.5; 11.9.0 to before 11.9.1 Vulnerable ·Mattermost

Remediation

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.10.0, 11.9.1, 11.8.5, 11.7.8

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-12985
  2. 2026-10-03 Alias added: GHSA-c92j-r2f4-67xg
  3. 2026-10-07 CVSS score added · NVD
  4. 2026-10-07 Priority changed: LOW → MEDIUM

References

Advisory 1

  • TI-2025-18933 Arbitrary file read in Mattermost Boards via import & export board archive CVSS 3.1CRITICAL 9.9
  • TI-2025-04465 Path Traversal Leading to RCE by Any Authenticated Mattermost User CVSS 3.1CRITICAL 9.9
  • TI-2017-14068 An issue was discovered in Mattermost Server before 3.6.2. CVSS 3.1CRITICAL 9.8
  • TI-2017-14060 An issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. CVSS 3.1CRITICAL 9.8
  • TI-2017-14048 An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. CVSS 3.1CRITICAL 9.8
  • TI-2025-14360 Arbitrary file read via block duplication in Mattermost Boards CVSS 3.1CRITICAL 9.9
See all 505 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences