CVE-2016-11063 Mattermost Server vulnerable to Cross-site Scripting through file preview feature

What is CVE-2016-11063?

CVE-2016-11063 is a medium-severity cross-site scripting vulnerability in Mattermost Mattermost Server, published on 19 Jun 2020. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

An issue was discovered in Mattermost Server before 3.5.1. XSS can occur via file preview.

Weakness: CWE-79

Which versions are affected by CVE-2016-11063?

3 open source packages ship an affected version, including github.com/mattermost/mattermost-server. It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2016-11063?

Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 3.5.1 or 3.5.1+incompatible.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2016-11063 being exploited?

There is no known exploitation of CVE-2016-11063 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost Server

• CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers Critical 9.9
• CVE-2025-12421 Account Takeover via Code Exchange Endpoint Critical 9.9
• CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User Critical 9.9
• CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards Critical 9.9
• CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive Critical 9.9

All Mattermost Mattermost Server vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-cffj-7w5c-jqjh, GO-2025-4045.