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

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-21 · updated 2026-10-26
Weakness: CWE-22

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.

Affected products

jupyter nbconvert: from 6.5.0 before 7.17.1 — fixed in 7.17.1

How to fix

Upgrade to a fixed version: jupyter nbconvert 7.17.1. Check the vendor advisory for mitigations.

References

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