# CVE-2025-12421

## Summary

- **CVE ID:** CVE-2025-12421
- **Severity:** CRITICAL
- **CVSS Score:** 9.9 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H)
- **CWE:** CWE-303
- **Published:** Nov 27, 2025
- **Last Modified:** Mar 13, 2026

## 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).

## Affected Products

- Mattermost — Mattermost (11.0.0)
- Mattermost — Mattermost (10.12.0)
- Mattermost — Mattermost (10.11.0)
- Mattermost — Mattermost (10.5.0)
- Mattermost — Mattermost (11.1.0)
- Mattermost — Mattermost (11.0.3)
- Mattermost — Mattermost (10.12.2)
- Mattermost — Mattermost (10.11.5)
- Mattermost — Mattermost (10.5.13)

## References

- [CNA](https://mattermost.com/security-updates)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.34%
- **EPSS Percentile:** 27.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._