rules:
  - id: auth.py.mcp.unauthenticated-server
    languages:
      - python
    severity: ERROR
    message: |
      This MCP server is exposed over a NETWORK transport (streamable-http /
      SSE) but was constructed with no authentication: no `auth=` and no
      `token_verifier=`. Its tools are reachable by anyone who can reach the
      port (CWE-306). A Knostic scan found none of ~2,000 internet-exposed MCP
      servers required auth; unauthenticated `/mcp` endpoints are the surface
      behind CVE-2026-66012 and the Q2-2026 MCP exposure wave.

      Require auth before serving over the network:
        mcp = FastMCP("name", token_verifier=verifier,
                      auth=AuthSettings(issuer_url=..., resource_server_url=..., required_scopes=[...]))
      (A `stdio` transport is local and out of scope for this rule.)
    # Fires on a network-transport call whose FastMCP/MCPServer instance was
    # created WITHOUT auth= or token_verifier=. stdio is intentionally excluded.
    patterns:
      - pattern-either:
          - pattern: '$M.run(transport="streamable-http")'
          - pattern: '$M.run(transport="sse")'
          - pattern: $M.streamable_http_app()
          - pattern: $M.sse_app()
      - pattern-either:
          - pattern-inside: |
              $M = FastMCP(...)
              ...
          - pattern-inside: |
              $M = MCPServer(...)
              ...
      - pattern-not-inside: |
          $M = $CTOR(..., auth=$A, ...)
          ...
      - pattern-not-inside: |
          $M = $CTOR(..., token_verifier=$V, ...)
          ...
    metadata:
      oauthlint-rule-id: AUTH-PY-MCP-003
      oauthlint-doc-url: https://oauthlint.dev/rules/py-mcp-unauthenticated-server
      category: security
      cwe: CWE-306
      owasp: API2:2023
      llm-prevalence: HIGH
      technology:
        - mcp
        - fastmcp
        - modelcontextprotocol
      references:
        - https://modelcontextprotocol.io/specification/2026-07-28/basic/authorization
        - https://healthsystemcio.com/2026/07/28/mcp-server-exposure-health-isac/