Advisories for Pypi/Fastmcp package

While testing the OAuth Proxy implementation, it was noticed that the server does not properly respect the resource parameter submitted by the client in the authorization and token request. Instead of issuing the token explicitly for this MCP server, the token is issued for the base_url passed to the OAuthProxy during initialization. Affected File: https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/auth/oauth_proxy.py#L828 Affected Code: self._jwt_issuer: JWTIssuer = JWTIssuer( issuer=str(self.base_url), audience=f"{str(self.base_url).rstrip('/')}/mcp", signing_key=jwt_signing_key, )

There was a recent CVE report on MCP: https://nvd.nist.gov/vuln/detail/CVE-2025-66416. FastMCP does not use any of the affected components of the MCP SDK directly. However, FastMCP versions prior to 2.14.0 did allow MCP SDK versions <1.23 that were vulnerable to CVE-2025-66416. Users should upgrade to FastMCP 2.14.0 or later.

A command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor

While setting up an oauth client, it was noticed that the callback page hosted by the client during the flow embeds user-controlled content without escaping or sanitizing it. This leads to a reflected Cross-Site-Scripting vulnerability.

FastMCP documentation covers the scenario where it is possible to use Entra ID or other providers for authentication. In this context, because Entra ID does not support Dynamic Client Registration (DCR), the FastMCP-hosted MCP server is acting as the authorization provider, as declared in the Protected Resource Metadata (PRM) document hosted on the server. For example, on a local MCP server, it may be hosted here: http://localhost:8000/.well-known/oauth-protected-resource And the JSON …