CVE-2025-62800: Jlowin Fastmcp

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Jlowin Fastmcp: before 2.13.0 (fixed in 2.13.0)

Published 2025-10-28. Last modified 2026-10-08.