🛡️ Sentinel: [HIGH] Fix SSRF bypass on DNS resolution failure

Modified `is_private_ip` in `app/utils/network.py` to fail securely by returning True (blocking the request) when a hostname cannot be resolved. The previous implementation failed open, creating a risk for Server-Side Request Forgery (SSRF) and DNS rebinding attacks.

Updated corresponding tests to expect the secure behavior.

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

app/utils/network.py

@@ -27,8 +27,8 @@ def is_private_ip(hostname: str) -> bool:
                     return True
             return False
         except (socket.gaierror, socket.error):
-            # Cannot resolve - allow for testing/development
-            # In production, DNS should work properly
-            # Log this for debugging
-            logger.warning(f"Could not resolve hostname: {hostname}")
-            return False  # Changed from True to False to allow external domains in tests
+            # Cannot resolve.
+            # Fail securely: block unresolved domains to prevent DNS rebinding
+            # and SSRF bypasses via unresolvable addresses.
+            logger.warning(f"Could not resolve hostname (blocking securely): {hostname}")
+            return True