R0idamcp

FastMCP has a Command Injection vulnerability - Gemini CLI

Server names containing shell metacharacters (e.g., `&`) can cause command injection on Windows when passed to `fastmcp install claude-code` or `fastmcp install gemini-cli`. These install paths use `subprocess.run()` with a list argument, but on Windows the target CLIs often resolve to `.cmd` wrappers that are executed through `cmd.exe`, which interprets metacharacters in the flattened command string. PoC: ```python from fastmcp import FastMCP mcp = FastMCP(name="test&calc") @mcp.tool def rol

FastMCP OAuth Proxy token reuse across MCP servers

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:** ```python self._jwt_issuer:

FastMCP updated to MCP 1.23+ due to CVE-2025-66416

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.

FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name

### Summary 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 ### Details 1. generate_cursor_deeplink(server_name, …) embeds server_name verbatim in a cursor://…?name= query string. 2. open_deeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start <deeplink>. 3. Any cmd metacharacter inside server_name (&, |, >, ^, …) escapes the start comma

FastMCP vulnerable to reflected XSS in client's callback page

### Summary 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. ### Details The affected code is located in *https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/client/oauth_callback.py*, which embeds all values passed to the `create_callback_html` function via the `message` parameter it into the callback pag

FastMCP Auth Integration Allows for Confused Deputy Account Takeover

### Summary FastMCP documentation [covers the scenario](https://gofastmcp.com/integrations/azure) 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 http://localhos