CVE-2025-12419: Account takeover on OAuth/OpenID-enabled servers

Severity: critical (CVSS 9.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-11-27 · updated 2026-10-19
Weakness: CWE-303

Description

Mattermost versions 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12, 11.0.x <= 11.0.3 fail to properly validate OAuth state tokens during OpenID Connect authentication which allows an authenticated attacker with team creation privileges to take over a user account via manipulation of authentication data during the OAuth completion flow. This requires email verification to be disabled (default: disabled), OAuth/OpenID Connect to be enabled, and the attacker to control two users in the SSO system with one of them never having logged into Mattermost.

Affected products

Mattermost: from 10.5.0 before 10.5.13; from 10.11.0 before 10.11.5; from 10.12.0 before 10.12.2; from 11.0.0 before 11.0.4 — fixed in 10.11.5, 10.12.2, 10.5.13, 11.0.4

How to fix

Upgrade to a fixed version: Mattermost 10.11.5, 10.12.2, 10.5.13, 11.0.4. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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