---
cve: "CVE-2025-12421"
severity: "CRITICAL"
cvss: 9.9
epss: "0.4%"
vendor: "Mattermost"
kev: false
exploited: false
published: "2025-11-27 18:15:46"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-11-09T16:24:47+01:00"
---

# CVE-2025-12421

> 9.9 CRITICAL

## Beschreibung

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).

## CNA-Record (Kanon, cvelistV5)

- CNA: **Mattermost**
- State: PUBLISHED
- Stand: 2026-02-26 16:07:25
- CNA-CVSS: **9.9** (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **none**
  - Automatable: **no**
  - Technical Impact: **total**

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Gering | warn |
| UI Interaktion | Keine | bad |
| S Scope | Verändert | bad |
| C Vertraulichkeit | Hoch | bad |
| I Integrität | Hoch | bad |
| A Verfügbarkeit | Hoch | bad |

## Schwachstellen-Klasse

- **CWE-303** — Incorrect Implementation of Authentication Algorithm
  The requirements for the product dictate the use of an established authentication algorithm, but the implementation of the algorithm is incorrect.

## Angriffsmuster (CAPEC)

- [CAPEC-90 — Reflection Attack in Authentication Protocol](https://capec.mitre.org/data/definitions/90.html) _(Severity: High)_

## Patch verfügbar (OSV)

- 288281e8cbf15260ad074b883a263b796cdb3e28 (Commit)
- 46b5c436bb3093cc1da3fa2455f93d4c52389eee (Commit)

## BSI-Hinweise (deutsch)

- [Mattermost Server: Mehrere Schwachstellen ermöglichen die Umgehung von Sicherheitsmaßnahmen](https://wid.cert-bund.de/portal/wid/sicherheitshinweis/WID-SEC-W-2025-2434) — _BSI-Einstufung: hoch_
  Ein entfernter, authentisierter Angreifer kann mehrere Schwachstellen im Mattermost Server ausnutzen, um Sicherheitsmaßnahmen zu umgehen und so eine Kontoübernahme durchzuführen.

## Referenzen

- <https://mattermost.com/security-updates>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/sicherheitsluecken/cve-2025-12421/) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_