CVE-2025-12421

Account Takeover via Code Exchange Endpoint

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).

We have discovered 62 live websites that are affected by CVE-2025-12421.

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Affected Software

Product  Mattermost
Category Message Boards
Vulnerable Domains62 live websites (15% of Mattermost install base)
Vulnerable Versions
  • from 10.5 through 10.5.12
  • from 10.11 through 10.11.4
  • from 10.12 through 10.12.1
  • from 11 through 11.0.2
Vulnerable Versions Count10 versions ( 15% of all versions)


Common Weakness Enumeration

CWE-303 Incorrect Implementation of Authentication Algorithm



Details

  • Published - Nov 27, 2025
  • Updated - Feb 26, 2026

Credits

  • daw10 (finder)

Website Distribution by Country

Number of websites using CVE-2025-12421
United States13 websites


Germany23 websites
GB9 websites
France3 websites
Czech Republic2 websites
Russia2 websites
Turkmenistan2 websites
Austria1 websites
Canada1 websites

Website Distribution by TLD

Number of websites using CVE-2025-12421
.org14 websites
.com13 websites
.de11 websites
.ru4 websites
.co.uk2 websites
.fr2 websites
.info2 websites
.net2 websites
.io1 websites
.pl1 websites

Vulnerable Versions

Vulnerable versions are highlighted in red

Websites affected by CVE-2025-12421

Top websites that are affected by CVE-2025-12421. Please click on the "Contact us" link to get more information.
DomainCountryRankContacts
***********.com Germany***,***
****.*******.com GB***,***
****.*******.org Germany*,***,***
***********.ru Russia*,***,***
****.*******.com Germany*,***,***
****.*********.org United States*,***,***
****.**************.de Germany*,***,***
*****.*************.org GB*,***,***
*******.org Germany*,***,***
******.*************.org GB**,***,***
See full domain list

FAQ

CVE-2025-12421 is Incorrect Implementation of Authentication Algorithm in Mattermost
A total of 62 websites have been identified as vulnerable to CVE-2025-12421, based on global website indexing conducted by WebTechSurvey.
The Mattermost is affected by the CVE-2025-12421 vulnerability.
Mattermost versions up to and including 11.0.2 are vulnerable to CVE-2025-12421.