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.
| Package (Ecosystem) | Introduced | Fixed | Limit |
|---|---|---|---|
| fastmcp(PyPI) | 0 | 2.13.0 | N/A |
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