Account Takeover via Code Exchange Endpoint

Summary

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).

Timeline

1. Nov 27, 2025, 5:47 PM UTCCVE published
2. Dec 2, 2025, 4:55 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Feb 26, 2026, 4:07 PM UTCRecord last updated

Affected versions

• Mattermost Mattermost

  From 11.0.0 · through 11.0.2; From 10.12.0 · through 10.12.1; From 10.11.0 · through 10.11.4; From 10.5.0 · through 10.5.12

• github.com/mattermost/mattermost/server/v8Go

  fixed in 8.0.0-20251022210333-acda1fb5dd46

• github.com/mattermost/mattermost-serverGo

  From 11.0.0 · fixed in 11.0.3

• github.com/mattermost/mattermost-serverGo

  From 10.12.0 · fixed in 10.12.2

• github.com/mattermost/mattermost-serverGo

  From 10.11.0 · fixed in 10.11.5

• github.com/mattermost/mattermost-serverGo

  From 10.5.0 · fixed in 10.5.13

• github.com/mattermost/mattermost-serverGo

  All versions

• github.com/mattermost/mattermost-server/v5Go

  All versions

• github.com/mattermost/mattermost-server/v6Go

  All versions

References 1