Rembg is a tool to remove images background. Prior to 2.0.75, a path traversal vulnerability in the rembg HTTP server allows unauthenticated remote attackers to read arbitrary files from the server's filesystem. By sending a crafted request with a malicious model_path parameter, an attacker can force the server to attempt loading any file as an ONNX model, revealing file existence, permissions, and potentially file contents through error messages. This vulnerability is fixed in 2.0.75.

Affected: PyPI: rembg

## Summary

A **path traversal vulnerability** in the rembg HTTP server allows unauthenticated remote attackers to read arbitrary files from the server's filesystem. By sending a crafted request with a malicious `model_path` parameter, an attacker can force the server to attempt loading any file as an ONNX model, revealing file existence, permissions, and potentially file contents through error messages.

**CWE IDs:** CWE-22 (Path Traversal), CWE-73 (External Control of File Name or Path)

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## Details

### Vulnerable Code Flow

The vulnerability exists in how the HTTP server handles the `extras` JSON parameter for custom model types (`u2net_custom`, `dis_custom`, `ben_custom`).

**1. Entry Point** - [`rembg/commands/s_command.py`](https://github.com/danielgatis/rembg/blob/main/rembg/commands/s_command.py#L191-L202)

```python def im_without_bg(content: bytes, commons: CommonQueryParams) -> Response: kwargs = {} if commons.extras: try: kwargs.update(json.loads(commons.extras)) # ❌ No validation except Exception: pass # ... session = new_session(commons.model, **kwargs) # Passes arbitrary kwargs ```

The `extras` parameter is parsed as JSON and passed directly to `new_session()` without any validation.

**2. Path Handling** - [`rembg/sessions/u2net_custom.py`](https://github.com/danielgatis/rembg/blob/main/rembg/sessions/u2net_custom.py#L79-L83)

```python @classmethod def download_models(cls, *args, **kwargs):…

Affected: PyPI: rembg

Rembg is a tool to remove images background. Prior to 2.0.75, a path traversal vulnerability in the rembg HTTP server allows unauthenticated remote attackers to read arbitrary files from the server's filesystem. By sending a crafted request with a malicious model_path parameter, an attacker can force the server to attempt loading any file as an ONNX model, revealing file existence, permissions, and potentially file contents through error messages. This vulnerability is fixed in 2.0.75.