GHSA-vv7q-7jx5-f767: FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability

Summary

GHSA-vv7q-7jx5-f767 affects the OpenAPIProvider in FastMCP, which parses OpenAPI specifications to expose internal APIs to MCP clients. The _build_url() method in fastmcp/utilities/openapi/director.py substitutes path parameter values into URL templates without URL-encoding, and urljoin() then resolves ../ sequences, letting an attacker reach arbitrary backend endpoints. Because requests carry the MCP provider's configured authorization headers, the flaw results in authenticated SSRF.

Mitigation

The source does not state a fix yet. Check the original advisory for updates.

Topics

• Model Context Protocol

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