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Mattermost fails to properly validate OAuth state tokens during OpenID Connect authentication

Critical severity GitHub Reviewed Published Nov 27, 2025 to the GitHub Advisory Database • Updated Dec 1, 2025

Package

gomod github.com/mattermost/mattermost-server (Go)

Affected versions

>= 10.12.0, < 10.12.2
>= 10.11.0, < 10.11.5
>= 10.5.0, < 10.5.13
>= 11.0.0, < 11.0.4

Patched versions

10.12.2
10.11.5
10.5.13
11.0.4
gomod github.com/mattermost/mattermost/server/v8 (Go)
< 8.0.0-20251028000919-d3ed703dc833
8.0.0-20251028000919-d3ed703dc833

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.

References

Published by the National Vulnerability Database Nov 27, 2025
Published to the GitHub Advisory Database Nov 27, 2025
Reviewed Dec 1, 2025
Last updated Dec 1, 2025

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(22nd percentile)

Weaknesses

Improper Authentication

When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Learn more on MITRE.

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. Learn more on MITRE.

CVE ID

CVE-2025-12419

GHSA ID

GHSA-3x39-62h4-f8j6

Source code

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