CSRF Bypass in Mattermost 10.x-11.x Enables Admin Policy Switch
CVE-2026-27659 Published on March 25, 2026
CSRF vulnerability in UpdateAccessControlPolicyActiveStatus endpoint
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to properly validate CSRF tokens in the /api/v4/access_control_policies/{policy_id}/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a crafted request.. Mattermost Advisory ID: MMSA-2026-00578
Vulnerability Analysis
CVE-2026-27659 can be exploited with network access, requires user interaction and a small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality and integrity, and no impact on availability.
Weakness Type
What is a Session Riding Vulnerability?
The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request. When a web server is designed to receive a request from a client without any mechanism for verifying that it was intentionally sent, then it might be possible for an attacker to trick a client into making an unintentional request to the web server which will be treated as an authentic request. This can be done via a URL, image load, XMLHttpRequest, etc. and can result in exposure of data or unintended code execution.
CVE-2026-27659 has been classified to as a Session Riding vulnerability or weakness.
Products Associated with CVE-2026-27659
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Affected Versions
Mattermost:- Version 11.2.0, <= 11.2.2 is affected.
- Version 10.11.0, <= 10.11.10 is affected.
- Version 11.4.0, <= 11.4.0 is affected.
- Version 11.3.0, <= 11.3.1 is affected.
- Version 11.5.0 is unaffected.
- Version 11.2.3 is unaffected.
- Version 10.11.11 is unaffected.
- Version 11.4.1 is unaffected.
- Version 11.3.2 is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.