CVE-2026-39377 — nbconvert
MEDIUMCVE-2026-39377 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in nbconvert. A fix is available for nbconvert — see the affected versions and patch details below.
nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39377.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
nbconvertReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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:
c. ExtractAttachmentsPreprocessor.enabled = False
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | nbconvert | ≥ 6.5.0&&< 7.17.1 | 7.17.1pip install --upgrade 'nbconvert==7.17.1' |
Affected Products
nbconvertjupyterDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nbconvert, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nbconvert to 7.17.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39377 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2026-39377 in your dependencies?
Find it across PyPI, including transitive dependencies.