GitHub Security Advisory: GHSA-98h9-4798-4q5v
Package: diffusers (PIP)
Severity: HIGH (CVSS 8.8)
CWE: CWE-94: Improper Control of Generation of Code ('Code Injection')
Vulnerable versions: < 0.38.0
Patched in: 0.38.0

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

Details:
### Impact

A `trust_remote_code` bypass in `DiffusionPipeline.from_pretrained` allows arbitrary remote code execution despite the user passing `trust_remote_code=False` (or omitting it, which is the default). The vulnerability has three variants, all sharing the same root cause — the `trust_remote_code` gate was implemented inside `DiffusionPipeline.download()` rather than at the actual dynamic-module load site, so any code path that bypassed or short-circuited `download()` also bypassed the security check:

1. **Cross-repo `custom_pipeline`.** `DiffusionPipeline.from_pretrained('repoA', custom_pipeline='attacker/repoB', trust_remote_code=False)` — the gate evaluated against `repoA`'s file list rather than `repoB`'s, so `repoB`'s `pipeline.py` was loaded and executed.
2. **Local snapshot + Hub `custom_pipeline`.** `DiffusionPipeline.from_pretrained('/local/snapshot', custom_pipeline='attacker/repoB', trust_remote_code=False)` — the local-path branch never invoked `download()`, so the gate was never reached and remote code from `repoB` executed.
3. **Local snapshot with custom components.** `DiffusionPipeline.from_pretrained('/local/snapshot', trust_remote_code=False)` where the snapshot contains custom component files (e.g. `unet/my_unet_model.py`) referenced from `model_index.json` — same root cause; the local path skipped `download()` and custom component code executed.

Silent remote code execution on the victim's machine. Anyone calling `DiffusionPipeline.from_pretrained` with custom pipelines is impacted.

### Patches

Yes. Fixed in **diffusers 0.38.0** via [PR #13448](https://github.com/huggingface/diffusers/pull/13448). All users on versions `< 0.38.0` should upgrade:

```bash
pip install --upgrade "diffusers>=0.38.0"
```

The fix moves the `trust_remote_code` gate out of `DiffusionPipeline.download()` and into `get_cached_module_file` in `src/diffusers/utils/dynamic_modules_utils.py`, which is the actual chokepoint for every dynamic module load (local, Hub, or community mirror). All three variants now raise `ValueError` instead of executing untrusted code.

### Workarounds

If upgrading immediately is not possible:

- Only call `from_pretrained` with `pretrained_model_name_or_path`, `custom_pipeline`, and local snapshot directories from fully trusted sources that have been audited.
- Do not pass `custom_pipeline=` pointing at a Hub repository different from the primary `pretrained_model_name_or_path` before reading its `pipeline.py`.
- Before calling `from_pretrained` on a local snapshot, inspect the snapshot for unexpected `*.py` files, especially under component subdirectories (`unet/`, `scheduler/`, etc.) and at the snapshot root.

These are mitigations, not fixes — the only complete remediation is upgrading to 0.38.0.

### Resources

- **Fix:** https://github.com/huggingface/diffusers/pull/13448
- **Original issue:** https://github.com/huggingface/diffusers/issues/13446
- **Release notes:** https://github.com/huggingface/diffusers/re