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CVE-2026-19076 Auth bypass in Mattermost

Medium 4.4 Published Updated

Attackers with valid OAuth tokens can take over SSO accounts by bypassing account type switch restrictions in Mattermost.

Exploited in the wild
Not known
Login needed
An administrator
Attackable
Over the internet
Victim action needed
Not needed
Fix
None listed

What is CVE-2026-19076?

CVE-2026-19076 is a medium-severity authentication bypass vulnerability in Mattermost Mattermost Server, published on 16 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.

Official 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

Weakness: CWE-863

Which versions are affected by CVE-2026-19076?

It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2026-19076?

No fix has been published for CVE-2026-19076 yet. Limit exposure of the affected software until one is available.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2026-19076 being exploited?

There is no known exploitation of CVE-2026-19076 in the wild and no public exploit code.

All Mattermost Mattermost Server vulnerabilities

Sources

Also known as GHSA-hhjm-mg95-jr6g.

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