CVE-2025-62800 – FastMCP vulnerable to reflected XSS in client’s callback page

CVE ID : CVE-2025-62800

Published : Oct. 28, 2025, 10:15 p.m. | 29 minutes ago

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.

Severity: 5.3 | MEDIUM

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