What’s Vulnerable › Vulnerabilities

CVE-2026-19076: Mattermost fails to reject OAuth application sessions in account type switch, allowing account takeover via bearer token

• Severity: medium (CVSS 4.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-16 · updated 2026-10-27
• Weakness: CWE-863

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

Affected products

• Mattermost: from 11.7.0 before 11.7.10; from 11.8.0 before 11.8.6; from 11.9.0 before 11.9.2; 11.10.0 (and their updates) — fixed in 11.7.10, 11.8.6, 11.9.2
• Mattermost: from 11.10.0 through 11.10.0; from 11.7.0 through 11.7.9; from 11.9.0 through 11.9.1; from 11.8.0 through 11.8.5

How to fix

Upgrade to a fixed version: Mattermost 11.7.10, 11.8.6, 11.9.2. Check the vendor advisory for mitigations.

References

• https://mattermost.com/security-updates

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