CVE-2026-39377: Nbconvert Path Traversal Vulnerability

MODERATE
Advisory Identifier: GHSA-4c99-qj7h-p3vg
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CVSS 6.5
CWE-73 CWE-22
Published
Advisory Summary

CVE-2026-39377 is a MODERATE (CVSS 6.5) path traversal vulnerability (CWE-73: External Control of File Name or Path) affecting Nbconvert libraries in the PyPI ecosystem. The issue involves nbconvert has an arbitrary file write via path traversal in cell attachment filenames. Remediation is available by upgrading affected packages to version 7.17.1.

CVE-2026-39377 at a Glance

CVE Identifier CVE-2026-39377
GHSA Identifier GHSA-4c99-qj7h-p3vg
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-73: External Control of File Name or Path
Affected Product Nbconvert
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-39377

To remediate this vulnerability, upgrade all affected Nbconvert dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

nbconvert fixed: 7.17.1 
pip install nbconvert>=7.17.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show nbconvert

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-39377, inspect your installed packages using pip:

pip show nbconvert

Analyze the terminal output to locate any version of Nbconvert in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 7.17.1), your application is affected.

Note: The pip show nbconvert command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-73: External Control of File Name or Path, where the product allows user input to control or influence paths or file names that are used in filesystem operations. In Nbconvert, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

# 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: ```python c. ExtractAttachmentsPreprocessor.enabled = False ```

CVE-2026-39377 Affected Nbconvert Versions

1 component(s)
Fixed Versions:
7.17.1
Product / Package Ecosystem Affected Versions Fixed Version
nbconvert
pypi/nbconvert
PyPI
≥ 6.5.0
< 7.17.1
7.17.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/jupyter/nbconvert/security/advisories/GHSA-4c99-qj7h-p3vg
NVD — CVE-2026-39377 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-39377
Nbconvert Source Repository REPOSITORY
https://github.com/jupyter/nbconvert
Nbconvert Release RELEASE
https://github.com/jupyter/nbconvert/releases/tag/v7.17.1

Frequently Asked Questions

What is CVE-2026-39377?
CVE-2026-39377 is a security vulnerability in Nbconvert involving nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames under CWE-73: External Control of File Name or Path.
Which Nbconvert versions are affected?
Affected versions include releases prior to 7.17.1 across affected packages: nbconvert.
What version fixes CVE-2026-39377?
Upgrading to 7.17.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is nbconvert affected?
Yes, nbconvert is affected in releases prior to 7.17.1. Upgrade your dependency to 7.17.1 or later.
What is the CVSS score of CVE-2026-39377?
CVE-2026-39377 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2026-39377?
CVE-2026-39377 is classified under CWE-73: 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.).
How can I check PyPI dependencies for CVE-2026-39377?
Run the dependency tree command: 'pip show nbconvert'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4c99-qj7h-p3vg",
  "modified" : "2026-04-21T17:18:18Z",
  "published" : "2026-04-21T17:18:18Z",
  "aliases" : [ "CVE-2026-39377" ],
  "summary" : "nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames",
  "details" : "# Arbitrary File Write via Path Traversal in Cell Attachment Filenames\n\n## Summary\n\nnbconvert 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.\n\n\n## Impact\n\nThis vulnerability allows writing files with arbitrary content to arbitrary filesystem locations, limited only by the permissions of the process running nbconvert. The attacker controls:\n- Full destination path (via `../` traversal)\n- Filename\n- File extension\n- File content\n\n## Patches\n\n- upgrade to nbconvert v7.17.1\n\n## Workarounds\n\ndisable ExtractAttachmentsPreprocessor by setting:\n\n```python\nc. ExtractAttachmentsPreprocessor.enabled = False\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nbconvert"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "6.5.0"
      }, {
        "fixed" : "7.17.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jupyter/nbconvert/security/advisories/GHSA-4c99-qj7h-p3vg"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-39377"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jupyter/nbconvert"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jupyter/nbconvert/releases/tag/v7.17.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-73" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-21T17:18:18Z",
    "nvd_published_at" : "2026-04-21T01:16:05Z"
  }
}