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TI-2026-75219 Aliases CVE-2026-19076GHSA-hhjm-mg95-jr6g

Mattermost lets OAuth tokens take over SSO accounts

Priority LOW 22CWE-863Published · Updated

Key facts

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

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-863.

Summary

Mattermost versions from 11.7.0 through 11.7.9, from 11.8.0 through 11.8.5, from 11.9.0 through 11.9.1 and 11.10.0 are affected. The account type switch endpoint fails to reject OAuth application sessions, an authorization flaw (CWE-863). An attacker holding a valid OAuth bearer token for a user can set their own password and detach the account from its identity provider, taking it over permanently.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to reject OAuth application sessions in the account type switch endpoint, which allows an attacker with a valid OAuth bearer token for a target user to permanently take over that user's SSO-backed account by setting an attacker-controlled password and detaching the account from its identity provider via a crafted request to POST /api/v4/users/login/switch.. Mattermost Advisory ID: MMSA-2026-00758

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00199 9th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.11.0, 11.10.1, 11.7.10 +2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

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

Affected products

VendorProductAffected versionsFixed inStatusSource
MattermostMattermost11.10.0 – 11.10.0; 11.7.0 – 11.7.9; 11.9.0 – 11.9.1; 11.8.0 – 11.8.511.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6Patch availableCNA
  • Mattermost VendorMattermost Affected 11.10.0 – 11.10.0; 11.7.0 – 11.7.9; 11.9.0 – 11.9.1; 11.8.0 – 11.8.5 Fixed in 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6 Patch available CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*11.7.0 to before 11.7.10; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2VulnerableMattermost
cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:*11.10.0VulnerableMattermost
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 11.7.0 to before 11.7.10; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2 Vulnerable ·Mattermost
  • cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:* Versions 11.10.0 Vulnerable ·Mattermost

Remediation

Upgrade to Mattermost 11.11.0, 11.10.1, 11.7.10, 11.9.2 or 11.8.6, which fix the flaw per Mattermost advisory MMSA-2026-00758.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.11.0, 11.10.1, 11.7.10, 11.9.2, 11.8.6

Timeline

  1. 2026-10-16 Threatist record created from CVE-2026-19076
  2. 2026-10-16 Alias added: GHSA-hhjm-mg95-jr6g
  3. 2026-10-27 CVSS score added · NVD

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