CVE-2026-39377 nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-39377?
CVE-2026-39377 is a medium-severity vulnerability in jupyter nbconvert, published on 21 Apr 2026.
Official 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.
Which versions are affected by CVE-2026-39377?
3 open source packages ship an affected version, including nbconvert. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nbconvert PyPI | From 6.5.0 | 7.17.1 |
nbconvert PyPI | From 6.5.0 | 7.17.1 |
nbconvert PyPI | From 6.5.0 | 7.17.1 |
Products include Jupyter Nbconvert.
How do I fix CVE-2026-39377?
Upgrade nbconvert to 7.17.1 or later.
Is CVE-2026-39377 being exploited?
There is no known exploitation of CVE-2026-39377 in the wild and no public exploit code.
Other vulnerabilities in jupyter nbconvert
Sources
Also known as CLEANSTART-2026-HY94755, CLEANSTART-2026-VM36250, DEBIAN-CVE-2026-39377, GHSA-4c99-qj7h-p3vg, PYSEC-2026-2229, UBUNTU-CVE-2026-39377.