---
cve: "CVE-2026-27656"
severity: "MEDIUM"
cvss: 5.7
epss: "18%"
vendor: "Mattermost"
kev: false
exploited: false
published: "2026-03-25 17:16:56"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-13T03:15:39+02:00"
---

# CVE-2026-27656

> 5.7 MEDIUM

## Beschreibung

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow.. Mattermost Advisory ID: MMSA-2026-00590

## CVSS-Vektor

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

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

## Patch verfügbar (OSV)

- e1a78d1e9111eb77008014c8fec345708c74e756 (Commit)
- eda9f2a1fe66177a6dd6e96d8294e50f9bf4228d (Commit)

## Referenzen

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

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-27656) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_