PYSEC-2026-1430

## Summary

A **path traversal vulnerability** exists in GuardDog's `safe_extract()` function that allows malicious PyPI packages to write arbitrary files outside the intended extraction directory, leading to **Arbitrary File Overwrite** and **Remote Code Execution** on systems running GuardDog.

**CWE:** CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Details

### Vulnerable Code

**File:** `guarddog/utils/archives.py`

```python elif zipfile.is_zipfile(source_archive): with zipfile.ZipFile(source_archive, "r") as zip: for file in zip.namelist(): # Note: zip.extract cleans up any malicious file name # such as directory traversal attempts This is not the # case of zipfile.extractall zip.extract(file, path=os.path.join(target_directory, file)) # ❌ VULNERABLE ```

### Root Cause

The comment about `zip.extract()` fooled me at first :) then I noticed the `os.path.join()` call. The vulnerability stems from **incorrect usage of Python's `zipfile.ZipFile.extract()` API**:

- The `path` parameter should be the **target directory**, not a full file path - `extract()` automatically appends the member name to the path - By passing `os.path.join(target_directory, file)`, GuardDog causes the filename to be appended **twice** - This breaks zipfile's built-in path traversal sanitization

### Attack Vector

1. Attacker creates malicious wheel with path traversal filenames 2. Uploads to PyPI or distributes directly 3. Package scan: `guarddog pypi scan malicious-pkg` 4. GuardDog downloads and extracts the package 5. Malicious files written to arbitrary locations 6. Code execution could be achieved

## Impact

Impact depends on how GuardDog is running and under which environment.

### Critical Scenarios

1. **Immediate Code Execution** - Write to `~/.bashrc` → executes on next shell - Write to `~/.profile` → executes on login

2. **Persistent Backdoors** - Write to `~/.ssh/authorized_keys` → SSH access - Write to `/etc/cron.d/malicious` → scheduled execution (if root) - Write to systemd user services → persistent execution

and more...

## Credits

**Reported by:** Charbel (dwbruijn)