Mattermost Server 10.11.x <= 10.11.13 / 11.5.x <= 11.5.1 Multiple Vulnerabilities (MMSA-2026-00570 / MMSA-2026-00575 / MMSA-2026-00582 / MMSA-2026-00622)

The version of Mattermost Server installed on the remote host is affected by multiple vulnerabilities: - Mattermost fails to validate the Host header when constructing response URLs for custom slash commands which allows an authenticated attacker to redirect slash command responses to an...

CVE-2026-4273

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a craft...

CVE-2026-4273

Mattermost contains an insufficient validation flaw in remote cluster invite confirmation. Versions affected: 11.5.x ≤ 11.5.1 and 10.11.x ≤ 10.11.13. The RefreshedToken is not properly checked against the original invite token, allowing an authenticated attacker to bypass token rotation and reuse...

CVE-2026-4273 Insufficient token rotation validation in remote cluster invite confirmation

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a craft...

CVE-2026-4273: Incorrect Authorization

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token rotation and reuse the original invite token via sending a craft...

CVE-2025-13324: Incorrect Authorization

Mattermost versions 10.11.x = 10.11.5, 11.0.x = 11.0.4, 10.12.x = 10.12.2 fail to invalidate remote cluster invite tokens when using the legacy version 1 protocol or when the confirming party does not provide a refreshed token, which allows an attacker who has obtained an invite token to...