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nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

Moderate severity GitHub Reviewed Published Apr 20, 2026 in jupyter/nbconvert • Updated Apr 21, 2026

Package

pip nbconvert (pip)

Affected versions

>= 6.5.0, < 7.17.1

Patched versions

7.17.1

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

References

@minrk minrk published to jupyter/nbconvert Apr 20, 2026
Published by the National Vulnerability Database Apr 21, 2026
Published to the GitHub Advisory Database Apr 21, 2026
Reviewed Apr 21, 2026
Last updated Apr 21, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(18th percentile)

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

External Control of File Name or Path

The product allows user input to control or influence paths or file names that are used in filesystem operations. Learn more on MITRE.

CVE ID

CVE-2026-39377

GHSA ID

GHSA-4c99-qj7h-p3vg

Source code

Credits

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