T05 · Unauthorized Access and Privilege Escalation
Error
- Location
- scripts/monitor_page.py:20
- Finding
- Unrestricted URL Fetching Enables SSRF and Local File Access## Vulnerability Details **File Location**: `scripts/monitor_page.py`, lines 20-24 **Vulnerability Type**: Server-Side Request Forgery and local resource access **Risk Level**: High ### Vulnerable Code ```python def fetch_page(url: str) -> str: try: import urllib.request req = urllib.request.Request(url, headers={"User-Agent": "Mozilla/5.0"}) with urllib.request.urlopen(req, timeout=10) as r: return r.read().decode("utf-8", errors="ignore") except Exception as e: return f"[ERROR fetching page: {e}]" ``` The value passed to this function originates directly from the required command-line argument: ```python p.add_argument("--url", required=True) ``` ### Technical Analysis The application passes an unrestricted, user-controlled URL to `urllib.request.urlopen()`. It does not validate the URL scheme, destination hostname, resolved IP address, port, or redirect chain. This allows a caller to request resources outside the intended scope of public webpage monitoring. Depending on the protocols supported by the runtime, requests can include local-file URLs as well as HTTP endpoints on loopback, private, link-local, or otherwise internal networks. The ten-second timeout limits request duration but does not prevent access to unauthorized destinations. Redirects also require validation because an apparently public URL could redirect to a prohibited internal address. ### Attack Path 1. An attacker or untrusted user controls the value supplied through `--url`. 2. The attacker supplies a local resource URL such as a `file://` URL, or an HTTP URL targeting a loopback, private-network, or cloud metadata service. 3. `fetch_page()` passes the value directly to `urllib.request.urlopen()`. 4. The request executes with the network reachability and file permissions of the monitoring process. 5. The returned content is processed as monitored page data. 6. `monitor()` ...[truncated 906 chars]
- Remediation
- ## Remediation Suggestions 1. Parse URLs before making requests and permit only explicitly required schemes, preferably `https` and, if necessary, `http`. 2. Reject URLs containing credentials or ambiguous hostname encodings. 3. Resolve the destination hostname and reject all loopback, private, link-local, multicast, unspecified, and reserved IPv4 and IPv6 addresses. 4. Apply the same validation after every DNS resolution and to every redirect destination. 5. Protect against DNS rebinding by connecting only to the validated resolved address while preserving the intended hostname for TLS verification. 6. Consider an explicit hostname allowlist when the intended monitoring targets are known. 7. Restrict destination ports to those required for webpage monitoring. 8. Run the monitor under a dedicated, least-privileged account with restricted filesystem and network access. 9. Return an explicit fetch failure instead of treating exception text as normal page content. 10. Add automated tests covering `file://`, loopback, private IPv4, private IPv6, link-local, encoded-address, and redirect-based bypass attempts.