# CVE-2025-12421: GO-2025-4170 - Mattermost fails to to verify the token used during code exchange in github.com/mattermost/mattermost-server

Source: https://junglewise.ai/threats/cve-2025-12421-mattermost-fails-to-to-verify-the-token-used-during-code-exchange  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-11-27  
License: CC BY 4.0 with a link back

CVE-2025-12421 · Severity: critical · CVSS 9.9 · Published 2025-11-27

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).

Technologies: [github.com/mattermost/mattermost-server (Go)](https://junglewise.ai/threats/technologies/github-com-mattermost-mattermost-server), [github.com/mattermost/mattermost-server/v5 (Go)](https://junglewise.ai/threats/technologies/github-com-mattermost-mattermost-server-v5), [github.com/mattermost/mattermost-server/v6 (Go)](https://junglewise.ai/threats/technologies/github-com-mattermost-mattermost-server-v6), [github.com/mattermost/mattermost/server/v8 (Go)](https://junglewise.ai/threats/technologies/github-com-mattermost-mattermost-server-v8), [Mattermost Server](https://junglewise.ai/threats/technologies/server-public). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Mattermost](https://junglewise.ai/threats/vendors/mattermost).

## Quick answers

**Is CVE-2025-12421 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-12421 being exploited in the wild.

**How severe is CVE-2025-12421?** Critical severity, with a CVSS score of 9.9, published 27 November 2025.

**Which products and versions are affected?** github.com/mattermost/mattermost-server (Go) SEMVER:introduced=0, SEMVER:introduced=11.0.0,fixed=11.0.3; github.com/mattermost/mattermost-server/v5 (Go) SEMVER:introduced=0; github.com/mattermost/mattermost-server/v6 (Go) SEMVER:introduced=0; github.com/mattermost/mattermost/server/v8 (Go) SEMVER:introduced=0,fixed=8.0.0-20251022210333-acda1fb5dd46.

**Is there a fix for CVE-2025-12421?** Yes. github.com/mattermost/mattermost-server (Go): upgrade to 11.0.3 or later; github.com/mattermost/mattermost/server/v8 (Go): upgrade to 8.0.0-20251022210333-acda1fb5dd46 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2025-12421?** Check whether you run github.com/mattermost/mattermost-server (Go), github.com/mattermost/mattermost-server/v5 (Go), github.com/mattermost/mattermost-server/v6 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/mattermost/mattermost-server (Go): upgrade to 11.0.3 or later

  ```sh
  go get github.com/mattermost/mattermost-server@v11.0.3
  ```

- github.com/mattermost/mattermost/server/v8 (Go): upgrade to 8.0.0-20251022210333-acda1fb5dd46 or later

  ```sh
  go get github.com/mattermost/mattermost/server/v8@v8.0.0-20251022210333-acda1fb5dd46
  ```


## Affected products

- github.com/mattermost/mattermost-server (Go) SEMVER:introduced=0, SEMVER:introduced=11.0.0,fixed=11.0.3
- github.com/mattermost/mattermost-server/v5 (Go) SEMVER:introduced=0
- github.com/mattermost/mattermost-server/v6 (Go) SEMVER:introduced=0
- github.com/mattermost/mattermost/server/v8 (Go) SEMVER:introduced=0,fixed=8.0.0-20251022210333-acda1fb5dd46
- Mattermost Server

## Identifiers

- CVE-2025-12421
- GHSA-mp6x-97xj-9x62
- GO-2025-4170

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