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BREW-jupyterlab-CVE-2026-39377 — nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

Affected: Homebrew: jupyterlab

# Arbitrary File Write via Path Traversal in Cell Attachment Filenames

## Summary

nbconvert allows arbitrary file writes to locations outside the intended output directory when processing notebooks containing crafted cell attachment filenames. The `ExtractAttachmentsPreprocessor` passes attachment filenames directly to the filesystem without sanitization, enabling path traversal attacks. This vulnerability provides complete control over both the destination path and file extension.

## Impact

This vulnerability allows writing files with arbitrary content to arbitrary filesystem locations, limited only by the permissions of the process running nbconvert. The attacker controls: - Full destination path (via `../` traversal) - Filename - File extension - File content

## Patches

- upgrade to nbconvert v7.17.1

## Workarounds

disable ExtractAttachmentsPreprocessor by setting:

```python c. ExtractAttachmentsPreprocessor.enabled = False ```

CVE-2026-39377 — nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

Affected: jupyter nbconvert

The nbconvert tool, jupyter nbconvert, converts Jupyter notebooks to various other formats via Jinja templates. Versions 6.5 through 7.17.0 allow arbitrary file writes to locations outside the intended output directory when processing notebooks containing crafted cell attachment filenames. The `ExtractAttachmentsPreprocessor` passes attachment filenames directly to the filesystem without sanitization, enabling path traversal attacks. This vulnerability provides complete control over both the destination path and file extension. Version 7.17.1 contains a patch.

GHSA-4c99-qj7h-p3vg — nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

Affected: PyPI: nbconvert