Mattermost 10-11.x Token Rotation Bypass via RefreshedToken Reuse
CVE-2026-4273 Published on May 18, 2026
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 crafted invite confirmation with a RefreshedToken matching the original token. Mattermost Advisory ID: MMSA-2026-00575
Vulnerability Analysis
CVE-2026-4273 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
What is an AuthZ Vulnerability?
The software performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
CVE-2026-4273 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-4273
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Affected Versions
Mattermost:- Version 11.5.0, <= 11.5.1 is affected.
- Version 10.11.0, <= 10.11.13 is affected.
- Version 11.6.0 is unaffected.
- Version 11.5.2 is unaffected.
- Version 10.11.14 is unaffected.