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

Source: https://junglewise.ai/threats/cve-2026-39377-nbconvert-has-an-arbitrary-file-write-via-path-traversal-in-cell  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-21. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

CVE-2026-39377 · Severity: medium · CVSS 6.5 · Published 2026-04-21

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.

Technologies: [Jupyter Nbconvert](https://junglewise.ai/threats/technologies/jupyter-nbconvert), [nbconvert (PyPI)](https://junglewise.ai/threats/technologies/nbconvert). Vendors: [Jupyter](https://junglewise.ai/threats/vendors/jupyter), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-39377 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-39377 being exploited in the wild.

**How severe is CVE-2026-39377?** Medium severity, with a CVSS score of 6.5, published 21 April 2026.

**Which products and versions are affected?** nbconvert (PyPI) >= 6.5.0, < 7.17.1, ECOSYSTEM:introduced=6.5.0,fixed=7.17.1.

**Is there a fix for CVE-2026-39377?** Yes. nbconvert (PyPI): upgrade to 7.17.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-39377?** Check whether you run Jupyter Nbconvert or nbconvert (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- nbconvert (PyPI): upgrade to 7.17.1 or later

  ```sh
  pip install "nbconvert>=7.17.1"
  ```


## Affected products

- Jupyter Nbconvert
- nbconvert (PyPI) >= 6.5.0, < 7.17.1, ECOSYSTEM:introduced=6.5.0,fixed=7.17.1

## Identifiers

- CVE-2026-39377
- GHSA-4c99-qj7h-p3vg
- PYSEC-2026-2229

## References

- [https://api.github.com/users/g0blinResearch](https://api.github.com/users/g0blinResearch)
- [https://github.com/g0blinResearch](https://github.com/g0blinResearch)
- [https://api.github.com/users/g0blinResearch/gists%7B/gist_id%7D](https://api.github.com/users/g0blinResearch/gists%7B/gist_id%7D)
- [https://api.github.com/users/g0blinResearch/repos](https://api.github.com/users/g0blinResearch/repos)
- [https://avatars.githubusercontent.com/u/11961962?v=4](https://avatars.githubusercontent.com/u/11961962?v=4)
- [https://api.github.com/users/g0blinResearch/events%7B/privacy%7D](https://api.github.com/users/g0blinResearch/events%7B/privacy%7D)

## Related threats

- [Jupyter nbconvert path traversal via output filename metadata](https://junglewise.ai/threats/cve-2026-114140-the-nbconvert-tool-jupyter-nbconvert-converts-jupyter-notebooks)
- [PYSEC-2026-1691 - nbconvert has an uncontrolled search path that leads to unauthorized code execution on Windows](https://junglewise.ai/threats/cve-2025-53000-nbconvert-has-an-uncontrolled-search-path-that-leads-to)
- [Jupyter nbconvert Cross-site Scripting in Mermaid HTML export](https://junglewise.ai/threats/cve-2026-6658-jupyter-nbconvert-cross-site-scripting-in-mermaid-html-export)
- [nbconvert has an Arbitrary File Read via Path Traversal in HTMLExporter Image Embedding](https://junglewise.ai/threats/cve-2026-39378-nbconvert-has-an-arbitrary-file-read-via-path-traversal-in)
- [nbconvert vulnerable to cross-site scripting (XSS) via multiple exploit paths](https://junglewise.ai/threats/cve-2021-32862-nbconvert-vulnerable-to-cross-site-scripting-xss-via-multiple)