CVE-2025-12419Network attack vector

Account takeover via ambiguous OAuth state parsing

Published Nov 27, 2025 · Updated Feb 26, 2026

Improper authentication in Mattermost allows remote authenticated users with team creation rights to take over another user account. AuthorizeOAuthUser compared a colon-concatenated email, action, and cookie string rather than parsing and matching each field, so delimiter-bearing authentication data could preserve the combined value while changing its fields. Exploitation requires OAuth/OpenID Connect, disabled email verification, team creation privileges, and control of two SSO users, including one that has never logged in.

CVSS severity9.9
Critical
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Mattermost allows remote authenticated users with team creation rights to take over another user account. AuthorizeOAuthUser compared a colon-concatenated email, action, and cookie string rather than parsing and matching each field, so delimiter-bearing authentication data could preserve the combined value while changing its fields. Exploitation requires OAuth/OpenID Connect, disabled email verification, team creation privileges, and control of two SSO users, including one that has never logged in.

The record

CVE
CVE-2025-12419
Published
Nov 27, 2025
Updated
Feb 26, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-303, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 27, 2025CVE publishedPublication date reported by the CVE source.
  2. Feb 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.11.0 <=10.11.4
  2. Affected versionversion=10.12.0 <=10.12.1
  3. Affected versionversion=10.5.0 <=10.5.12
  4. Affected versionversion=11.0.0 <=11.0.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.4; version=10.12.0 <=10.12.1; version=10.5.0 <=10.5.12; version=11.0.0 <=11.0.3

Published CVSS scores

9.9Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-303Incorrect Implementation of Authentication Algorithm
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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