From dcde79b6b0aa7a8bb51a8da005268186e6e44c09 Mon Sep 17 00:00:00 2001
From: Charan Rathore <charan-rathore@users.noreply.github.com>
Date: Mon, 28 Sep 2026 10:19:32 +0530
Subject: [PATCH] fix: require JSON object for adapter chat passthrough

---
 .../pass_through_endpoints.py                 | 11 ++--
 .../test_pass_through_endpoints.py            | 60 +++++++++++++++++++
 2 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py b/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py
index e0a4184291e..a7a6ea6863a 100644
--- a/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py
+++ b/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py
@@ -1,4 +1,3 @@
-import ast
 import asyncio
 import copy
 import json
@@ -220,11 +219,13 @@ async def chat_completion_pass_through_endpoint(
     data = {"litellm_call_id": litellm_call_id}
     try:
         body: Final = await request.body()
-        body_str: Final = body.decode()
         try:
-            data = ast.literal_eval(body_str) | data
-        except Exception:
-            data = json.loads(body_str) | data
+            parsed_body: Final = json.loads(body)
+        except (UnicodeDecodeError, json.JSONDecodeError) as exc:
+            raise HTTPException(status_code=400, detail="Request body must be valid JSON") from exc
+        if not isinstance(parsed_body, dict):
+            raise HTTPException(status_code=400, detail="Request body must be a JSON object")
+        data = parsed_body | data
 
         data["adapter_id"] = adapter_id
 
diff --git a/tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py b/tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py
index 3469df082e0..ade94276604 100644
--- a/tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py
+++ b/tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py
@@ -7481,6 +7481,66 @@ def test_passthrough_sees_the_public_list_rebound_after_import(monkeypatch: pyte
     assert split.forwarded_body == {"contents": [{"parts": [{"text": "hi"}]}]}
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "body",
+    (
+        b"{'model': 'gpt-4o-mini'}",
+        b'(1, 2, {"role": "user"})',
+        b"[1, 2]",
+        b'{"model":',
+    ),
+)
+async def test_adapter_chat_rejects_non_object_or_non_json_body(monkeypatch: pytest.MonkeyPatch, body: bytes):
+    proxy_logging = MagicMock()
+    proxy_logging.post_call_failure_hook = AsyncMock()
+    add_request_data = AsyncMock()
+    monkeypatch.setattr("litellm.proxy.proxy_server.proxy_logging_obj", proxy_logging)
+    monkeypatch.setattr("litellm.proxy.proxy_server.add_litellm_data_to_request", add_request_data)
+    request = MagicMock(spec=Request)
+    request.body = AsyncMock(return_value=body)
+
+    with pytest.raises(ProxyException) as raised:
+        await chat_completion_pass_through_endpoint(
+            fastapi_response=Response(),
+            request=request,
+            adapter_id="anthropic",
+            user_api_key_dict=UserAPIKeyAuth(api_key="sk-test"),
+        )
+
+    assert (raised.value.type, raised.value.code) == ("invalid_request_error", "400")
+    add_request_data.assert_not_awaited()
+
+
+@pytest.mark.asyncio
+async def test_adapter_chat_accepts_json_object(monkeypatch: pytest.MonkeyPatch):
+    proxy_logging = MagicMock()
+    proxy_logging.pre_call_hook = AsyncMock(side_effect=lambda **kwargs: kwargs["data"])
+    proxy_logging.post_call_failure_hook = AsyncMock()
+
+    async def add_request_data(**kwargs: object) -> object:
+        return kwargs["data"]
+
+    monkeypatch.setattr("litellm.proxy.proxy_server.proxy_logging_obj", proxy_logging)
+    monkeypatch.setattr("litellm.proxy.proxy_server.add_litellm_data_to_request", add_request_data)
+    monkeypatch.setattr("litellm.proxy.proxy_server.llm_router", None)
+    monkeypatch.setattr("litellm.proxy.proxy_server.user_model", None)
+    monkeypatch.setattr("litellm.proxy.proxy_server.general_settings", {})
+    request = MagicMock(spec=Request)
+    request.body = AsyncMock(return_value=b'{"model":"unknown-model","messages":[]}')
+
+    with pytest.raises(ProxyException) as raised:
+        await chat_completion_pass_through_endpoint(
+            fastapi_response=Response(),
+            request=request,
+            adapter_id="anthropic",
+            user_api_key_dict=UserAPIKeyAuth(api_key="sk-test"),
+        )
+
+    assert (raised.value.type, raised.value.code) == ("invalid_request_error", "400")
+    assert proxy_logging.pre_call_hook.await_args.kwargs["data"]["model"] == "unknown-model"
+
+
 @pytest.mark.asyncio
 async def test_chat_completion_pass_through_endpoint_answers_an_openai_typed_error_for_an_unknown_model(
     monkeypatch: pytest.MonkeyPatch,