CVE-2026-9571 PUBLISHED

Deactivated user accounts can continue to obtain valid OAuth access tokens via refresh token grant in Mattermost

Assigner: Mattermost
Reserved: 26.05.2026 Published: 13.07.2026 Updated: 13.07.2026

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to invalidate OAuth refresh tokens upon user account deactivation, which allows a deactivated user or an attacker in possession of a valid refresh token to obtain new functional access tokens via the OAuth refresh token grant endpoint.. Mattermost Advisory ID: MMSA-2026-00680

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:N
CVSS Score: 5.9

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	High
Privileges Required	High	Integrity Impact	High
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.7.0 to 11.7.2 (incl.) affected from 11.6.0 to 11.6.4 (incl.) affected from 10.11.0 to 10.11.19 (incl.) Version 11.8.0 is unaffected Version 11.7.3 is unaffected Version 11.6.5 is unaffected Version 10.11.20 is unaffected

Solutions

Update Mattermost to versions 11.8.0, 11.7.3, 11.6.5, 10.11.20 or higher.

Credits

kirs112 finder

References

MMSA-2026-00680

Problem Types

CWE-305 – Authentication Bypass by Primary Weakness CWE