fix(proxy): reject non-object JSON request bodies

litellm/proxy/common_utils/http_parsing_utils.py

@@ -208,6 +208,14 @@ async def _read_request_body(request: Request | None) -> dict:
                             code=status.HTTP_400_BAD_REQUEST,
                         )
 
+        if not isinstance(parsed_body, dict):
+            raise ProxyException(
+                message="JSON request body must be an object",
+                type="invalid_request_error",
+                param="request_body",
+                code=status.HTTP_400_BAD_REQUEST,
+            )
+
         # Cache the parsed result
         _safe_set_request_parsed_body(request=request, parsed_body=parsed_body)
         return parsed_body

tests/test_litellm/proxy/common_utils/test_http_parsing_utils.py

@@ -46,6 +46,19 @@ def _starlette_request(body: bytes, content_type: str) -> Request:
     return Request(scope, receive)
 
 
+@pytest.mark.parametrize("body", [b"[]", b"123", b'"str"', b"true", b"null"])
+@pytest.mark.asyncio
+async def test_read_request_body_rejects_non_object_json(body: bytes):
+    request = _starlette_request(body, "application/json")
+
+    with pytest.raises(ProxyException) as error:
+        await _read_request_body(request)
+
+    assert error.value.code == "400"
+    assert "JSON request body must be an object" in error.value.message
+    assert _safe_get_request_parsed_body(request) is None
+
+
 @pytest.mark.asyncio
 async def test_read_raw_json_body_returns_the_bytes_the_parsed_body_came_from():
     body = b'{"model": "claude-sonnet-4-5", "messages": [{"role": "user", "content": "hi"}]}'