CVE-2025-62800
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-10-28

Last updated on: 2025-11-07

Assigner: GitHub, Inc.

Description
FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0 have a reflected cross-site scripting vulnerability in the OAuth client callback page (oauth_callback.py) where unescaped user-controlled values are inserted into the generated HTML, allowing arbitrary JavaScript execution in the callback server origin. The issue is fixed in version 2.13.0.
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Meta Information
Published
2025-10-28
Last Modified
2025-11-07
Generated
2026-06-16
AI Q&A
2025-10-28
EPSS Evaluated
2026-06-15
NVD
CVE-2025-62800
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
jlowin fastmcp to 2.13.0 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-79 The product 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.
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Executive Summary

This vulnerability is a reflected cross-site scripting (XSS) issue in FastMCP versions prior to 2.13.0. It occurs in the OAuth client callback page (oauth_callback.py) where user-controlled values are inserted into the HTML without proper escaping. This allows an attacker to execute arbitrary JavaScript code in the context of the callback server's origin.

Impact Analysis

An attacker exploiting this vulnerability can execute arbitrary JavaScript in the context of the affected server, potentially leading to session hijacking, theft of sensitive information, or performing actions on behalf of the user without their consent.

Mitigation Strategies

Upgrade FastMCP to version 2.13.0 or later, as this version contains the fix for the reflected cross-site scripting vulnerability in the OAuth client callback page.

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