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EUVD-2026-274294

fkie_cve-2026-27905

BentoML is a Python library for building online serving systems optimized for AI apps and model inference. Prior to 1.4.36, the safe_extract_tarfile() function validates that each tar member's path is within the destination directory, but for symlink members it only validates the symlink's own path, not the symlink's target. An attacker can create a malicious bento/model tar file containing a symlink pointing outside the extraction directory, followed by a regular file that writes through the symlink, achieving arbitrary file write on the host filesystem. This vulnerability is fixed in 1.4.36.

GHSA-m6w7-qv66-g3mf — BentoML Vulnerable to Arbitrary File Write via Symlink Path Traversal in Tar Extraction

Affected: PyPI: bentoml

# Arbitrary File Write via Symlink Path Traversal in Tar Extraction

## Summary

The `safe_extract_tarfile()` function validates that each tar member's path is within the destination directory, but for symlink members it only validates the symlink's own path, **not the symlink's target**. An attacker can create a malicious bento/model tar file containing a symlink pointing outside the extraction directory, followed by a regular file that writes through the symlink, achieving arbitrary file write on the host filesystem.

## Affected Component

- **File**: `src/bentoml/_internal/utils/filesystem.py:58-96` - **Callers**: `src/bentoml/_internal/cloud/bento.py:542`, `src/bentoml/_internal/cloud/model.py:504` - **Affected versions**: All versions with `safe_extract_tarfile()`

## Severity

**CVSS 3.1: 8.1 (High)** `AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H`

## Vulnerability Details

### Vulnerable Code (filesystem.py:58-96)

```python def safe_extract_tarfile(tar, destination): os.makedirs(destination, exist_ok=True) for member in tar.getmembers(): fn = member.name path = os.path.abspath(os.path.join(destination, fn)) if not Path(path).is_relative_to(destination): # Line 64: INCOMPLETE continue # Only checks member path, NOT symlink target if member.issym(): tar._extract_member(member, path) # Line 75: Creates symlink with UNVALIDATED target else: fp = tar.extractfile(member) with open(pa…

PYSEC-2026-2398 — BentoML Vulnerable to Arbitrary File Write via Symlink Path Traversal in Tar Extraction