CVE-2026-19076
Received Received - Intake

OAuth Session Takeover in Mattermost

Publication date: 2026-10-16

Last updated on: 2026-10-16

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to reject OAuth application sessions in the account type switch endpoint, which allows an attacker with a valid OAuth bearer token for a target user to permanently take over that user's SSO-backed account by setting an attacker-controlled password and detaching the account from its identity provider via a crafted request to POST /api/v4/users/login/switch.. Mattermost Advisory ID: MMSA-2026-00758

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Meta Information

Published
2026-10-16
Last Modified
2026-10-16
Generated
2026-10-16
AI Q&A
2026-10-16
EPSS Evaluated
N/A
NVD
CVE-2026-19076
EUVD
EUVD-2026-102747

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
Mattermost Mattermost 11.10.0
Mattermost Mattermost 11.7.0
Mattermost Mattermost 11.9.0
Mattermost Mattermost 11.8.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-863 The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.

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Executive Summary

Mattermost versions between 11.7.9 and 11.10.0 have a flaw where OAuth application sessions are not properly rejected during account type switching. An attacker with a valid OAuth token can take over a user's SSO-backed account by setting a new password and detaching the account from its identity provider through a crafted request to POST /api/v4/users/login/switch.

Impact Analysis

If you use Mattermost with SSO authentication in affected versions, an attacker could gain full control of your account. This includes accessing sensitive data, impersonating you, and performing actions on your behalf without needing to bypass SSO authentication.

Mitigation Strategies

Update Mattermost to a version that patches this vulnerability. Specifically, upgrade to versions beyond 11.10.0, 11.7.9, 11.9.1, or 11.8.5 depending on your current installation.

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