Mattermost <11.5.1/10.11.13: XSS via unescaped config vars in error pages
CVE-2026-3495 Published on May 18, 2026
Unescaped variables during error page composition
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to escape some variables that could contain malicious content during error page composition which allows an attacker with access to edit some site configuration to execute some malicious code via injecting some JS as part of those values.. Mattermost Advisory ID: MMSA-2026-00622
Vulnerability Analysis
CVE-2026-3495 can be exploited with network access, and requires 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 XSS Vulnerability?
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
CVE-2026-3495 has been classified to as a XSS vulnerability or weakness.
Products Associated with CVE-2026-3495
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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.