CVE-2026-44827

Diffusers has a `trust_remote_code` bypass via `custom_pipeline` and local custom components

Published

2026-05-07

Modified

2026-07-23

EPSS percentile

43%

Aliases

GHSA-j7w6-vpvq-j3gm

Sources

github-advisory

Summary

## Background This vulnerability is found in the `DiffusionPipeline.from_pretrained` flow, which is used to load a pipeline from the HuggingFace Hub. This function accepts an optional `custom_pipeline` keyword argument: the name of a Python file in the repo that contains a custom class inheriting from `DiffusionPipeline`. An equivalent flow is triggered when the `_class_name` field in `model_index.json` (the repo config file) is set to a custom class. Any attempt to use a custom pipeline throws the following exception, requesting that `trust_remote_code` is also passed: ```python DiffusionPipeline.from_pretrained( pretrained_model_name_or_path='ido-shani/custom-pipeline', custom_pipeline="custom" ) ValueError: The repository for ido-shani/custom-pipeline contains custom code in custom.py which must be executed to correctly load the model. You can inspect the repository content at https://hf.co/ido-shani/custom-pipeline/blob/main/custom.py. Please pass the argument `trust_remote_code=True` to allow custom code to be run. ``` The vulnerability is a silent RCE - it allows arbitrary code to be loaded through the custom\_pipeline flow from a Hub repo, with no `custom_pipeline` or `trust_remote_code` kwargs and nothing suspicious in the config. The `from_pretrained` call succeeds and returns a functional pipeline. ## Naive Flow First, all relevant arguments are popped from kwargs and stored in local variables. Given a `pretrained_model_name_or_path` that is a Hub repo ID, `DiffusionPipeline.download()` is called. This function serves two roles: it orchestrates downloading relevant model files, and it is the security gatekeeper for `trust_remote_code`. It is called even if the model is already cached; in that case it exits early. If the repo contains custom code, it checks whether `trust_remote_code` was passed and raises otherwise: ```python # pipeline_utils.py:1645-1652 load_pipe_from_hub = custom_pipeline is not None and f"{custom_pipeline}.py" in filenames ... if load_pipe_from_hub and not trust_remote_code: raise ValueError(...) ``` It then runs `_get_pipeline_class`, which returns the class object of the pipeline in order to inspect its `__init__` signature and determine which component files need to be downloaded. As part of building the `allow_patterns` list used to filter the snapshot download to necessary files only, the custom pipeline file is explicitly included if present: ```python # pipeline_utils.py:1707 allow_patterns += [f"{custom_pipeline}.py"] if f"{custom_pipeline}.py" in filenames else [] ``` The function then checks if all expected files are already present, and either exits early or triggers a snapshot download with those patterns. The next step in `from_pretrained` is loading the pipeline class a second time, this time to actually instantiate it. Before calling `_get_pipeline_class` again, `_resolve_custom_pipeline_and_cls` is called to translate the `custom_pipeline` name into a local path, since the files have already been downloaded: ```python # pipeline_loading_utils.py:965-974 def _resolve_custom_pipeline_and_cls(folder, config, custom_pipeline): custom_class_name = None if os.path.isfile(os.path.join(folder, f"{custom_pipeline}.py")): custom_pipeline = os.path.join(folder, f"{custom_pipeline}.py") elif isinstance(config["_class_name"], (list, tuple)) and os.path.isfile( os.path.join(folder, f"{config['_class_name'][0]}.py") ): custom_pipeline = os.path.join(folder, f"{config['_class_name'][0]}.py") custom_class_name = config["_class_name"][1] return custom_pipeline, custom_class_name ``` When `custom_class_name` is `None` (i.e. `custom_pipeline` was given as a kwarg rather than via the config), `_get_pipeline_class` will scan the file and automatically identify the class that subclasses `DiffusionPipeline`. Once this is done, `_get_pipeline_class` is invoked with the resolved local path, which loads the custom code, retr

Affected packages

Remediation: Upgrade to 0.38.0 or later.

References

• https://github.com/advisories/GHSA-j7w6-vpvq-j3gm