CVE-2017-18903 Mattermost Server vulnerable to CSRF if CORS is enabled

What is CVE-2017-18903?

CVE-2017-18903 is a high-severity 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 4.0.0, 3.10.2, and 3.9.2. CSRF can occur if CORS is enabled.

Weakness: CWE-352

Which versions are affected by CVE-2017-18903?

5 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-2017-18903?

Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 3.9.2+incompatible, 3.10.2+incompatible, 3.9.2 or 3.10.2.

Is CVE-2017-18903 being exploited?

There is no known exploitation of CVE-2017-18903 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-fcwg-45jh-5qhf, GO-2026-4305.