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

.jules/sentinel.md

@@ -12,3 +12,8 @@
 **Vulnerability:** The `/radio/proxy/{stream_id}` endpoint in `backend/routers/radio.py` accepted stream URLs from the database (which can be created via user input on `/radio/streams`) and fetched them without validating the URL resolved to a safe external IP. It only checked `url.startswith(("http://", "https://"))`. This created a Server-Side Request Forgery (SSRF) vulnerability.
 **Learning:** Checking URL scheme prefixes is insufficient for SSRF protection. If the input allows internal hostnames (e.g., `localhost`) or private IPs, an attacker can proxy requests to internal services through the backend. This is particularly dangerous for proxy endpoints which return the response content.
 **Prevention:** Always use centralized SSRF validation (e.g., `validate_safe_url`) to check URLs against a strict list of allowed schemes and block private, loopback, or link-local IP addresses before making any outbound HTTP requests.
+
+## 2025-05-21 - [SSRF via Unvalidated Redirects in proxy_stream]
+**Vulnerability:** The `/radio/proxy/{stream_id}` endpoint instantiated an `httpx.AsyncClient` with `follow_redirects=True`. Although the initial user-provided URL was checked against SSRF using `validate_safe_url`, if the server responded with an HTTP redirect (e.g. 302 Found) to an internal URL, the client would follow it without re-validating the target URL, leading to an SSRF vulnerability.
+**Learning:** Checking a URL before making a request is insufficient if the HTTP client automatically follows redirects to new URLs. Each redirect target must also be validated against SSRF rules.
+**Prevention:** If `follow_redirects=True` must be used, add an `event_hooks={'request': [_validate_request_url]}` hook to `httpx.AsyncClient` to intercept and validate every outbound request URL during the lifecycle of the client, including redirects.

backend/routers/radio.py

@@ -383,7 +383,18 @@ async def proxy_stream(
     except ValueError as e:
         raise HTTPException(400, f"Invalid or unsafe stream URL: {str(e)}")
 
-    client = httpx.AsyncClient(timeout=httpx.Timeout(connect=10.0, read=None, write=10.0, pool=10.0), follow_redirects=True)
+    async def _validate_request_url(request: httpx.Request):
+        try:
+            validate_safe_url(str(request.url))
+        except ValueError as e:
+            # We raise a RequestError here so httpx catches it instead of crashing.
+            raise httpx.RequestError(f"SSRF validation failed: {e}", request=request)
+
+    client = httpx.AsyncClient(
+        timeout=httpx.Timeout(connect=10.0, read=None, write=10.0, pool=10.0),
+        follow_redirects=True,
+        event_hooks={'request': [_validate_request_url]},
+    )
     try:
         req = client.build_request("GET", stream.url)
         resp = await client.send(req, stream=True)