Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to to verify that the token used during the code exchange originates from the same authentication flow, which allows an authenticated user to perform account takeover via a specially crafted email address used when switching authentication methods and sending a request to the /users/login/sso/code-exchange endpoint. The vulnerability requires ExperimentalEnableAuthenticationTransfer to be enabled (default: enabled) and RequireEmailVerification to be disabled (default: disabled).
Advisories
Source ID Title
Github GHSA Github GHSA GHSA-mp6x-97xj-9x62 Mattermost fails to to verify the token used during code exchange
Fixes

Solution

Update Mattermost to versions 11.1.0, 11.0.3, 10.12.2, 10.11.5, 10.5.13 or higher.


Workaround

No workaround given by the vendor.

References
History

Fri, 28 Nov 2025 15:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Fri, 28 Nov 2025 09:00:00 +0000

Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost
Vendors & Products Mattermost
Mattermost mattermost

Thu, 27 Nov 2025 18:00:00 +0000

Type Values Removed Values Added
Description Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to to verify that the token used during the code exchange originates from the same authentication flow, which allows an authenticated user to perform account takeover via a specially crafted email address used when switching authentication methods and sending a request to the /users/login/sso/code-exchange endpoint. The vulnerability requires ExperimentalEnableAuthenticationTransfer to be enabled (default: enabled) and RequireEmailVerification to be disabled (default: disabled).
Title Account Takeover via Code Exchange Endpoint
Weaknesses CWE-303
References
Metrics cvssV3_1

{'score': 9.9, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: Mattermost

Published:

Updated: 2025-11-28T14:52:19.096Z

Reserved: 2025-10-28T16:54:12.491Z

Link: CVE-2025-12421

cve-icon Vulnrichment

Updated: 2025-11-28T14:52:13.431Z

cve-icon NVD

Status : Undergoing Analysis

Published: 2025-11-27T18:15:46.223

Modified: 2025-11-28T23:11:55.537

Link: CVE-2025-12421

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2025-11-28T08:51:18Z