🛡️ Sentinel: [HIGH] Fix SSRF bypass via HTTP redirects in url_upload

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

.jules/sentinel.md

@@ -19,3 +19,8 @@
 **Vulnerability:** The `_test_imap_connection` and `_test_s3_connection` functions in `app/api/integrations.py` did not validate user-provided `host` and `endpoint_url` variables against `is_private_ip()`. This allowed an attacker to test the presence of internal IMAP servers or direct S3 SDK API calls to internal infrastructure via SSRF.
 **Learning:** Any time a new generic connection or integration test is added, SSRF validation may be forgotten if the core network utility (`is_private_ip`) is not systematically applied to all outbound network operations, regardless of the protocol (e.g., IMAP, S3).
 **Prevention:** Establish a pattern where any user-configurable host or endpoint URL is immediately passed through the centralized `is_private_ip` validation function before any network call or third-party client initialization.
+
+## 2024-05-27 - SSRF Bypass via HTTP Redirects
+**Vulnerability:** In `app/api/url_upload.py`, the `validate_url_safety` function was correctly verifying the initially requested URL to prevent fetching internal IPs or cloud metadata endpoints. However, the subsequent `httpx.AsyncClient` was configured with `follow_redirects=True` without validating the destination of those redirects. An attacker could bypass SSRF protections by providing a URL to an attacker-controlled server that responds with a 301/302 redirect pointing to an internal target (e.g., `http://127.0.0.1` or `http://169.254.169.254`).
+**Learning:** Checking the URL before sending the request is insufficient if the HTTP client automatically follows redirects. The target of every single redirect must be subject to the same strict validation as the initial request.
+**Prevention:** Avoid `follow_redirects=True` for user-provided URLs when possible. If redirects must be followed, attach an event hook (e.g., `event_hooks={"response": [hook_function]}`) to the `httpx` client to intercept the response, calculate the redirect destination from the `Location` header, and run the URL safety validation logic before the redirect is actually followed.

app/api/url_upload.py

@@ -106,6 +106,25 @@ def validate_file_type(content_type: str, filename: str) -> bool:
     return False
 
 
+async def verify_redirect(response: httpx.Response) -> None:
+    """
+    Event hook to intercept redirects and validate the new destination URL.
+    Prevents SSRF bypasses via redirects to internal networks or metadata endpoints.
+    """
+    if response.status_code in (301, 302, 303, 307, 308):
+        location = response.headers.get("Location")
+        if location:
+            # Resolve relative redirects
+            new_url = str(response.url.join(location))
+            # Validate the new URL
+            try:
+                validate_url_safety(new_url)
+            except HTTPException as e:
+                # Map the validation error to an httpx exception so it can be handled
+                # properly by the caller, avoiding raw HTTPExceptions escaping the client scope
+                raise httpx.RequestError(f"Redirect to unsafe URL blocked: {e.detail}", request=response.request) from e
+
+
 @router.post("/process-url")
 @require_login
 async def process_url(
@@ -165,6 +184,7 @@ async def process_url(
             headers={
                 "User-Agent": "DocuElevate/1.0",  # Identify ourselves
             },
+            event_hooks={"response": [verify_redirect]},
         ) as client:
             async with client.stream("GET", url) as response:
                 response.raise_for_status()