Jupyter nbconvert path traversal flaw lets attackers write files anywhere

Jupyter nbconvert contains a high-severity path traversal vulnerability that allows attackers to write files to arbitrary locations on a victim's system. The issue affects versions 5.4.0 through 7.17.1 and is tracked as CVE-2026-114140 with a CVSS score of 8.8.

What happened

The nbconvert tool converts Jupyter notebooks into formats such as markdown, LaTeX, reStructuredText, or AsciiDoc using Jinja templates. According to the National Vulnerability Database record, the ExtractOutputPreprocessor component joins attacker-controlled cell output metadata filenames to the output directory without restricting the result to that specific directory. This lack of validation allows path traversal attacks that write attacker-controlled data to any location accessible to the victim user.

The vulnerability is present in Jupyter nbconvert versions starting from 5.4.0 and continuing until version 7.17.2. The source material states that this issue is fixed in version 7.17.2. Merely converting the supplied notebook does not require running the notebook cell again to trigger the malicious output metadata replacement. The flaw is classified under CWE-22, which relates to path traversal weaknesses.

Why it matters

A CVSS score of 8.8 indicates a high severity risk for organizations using Jupyter notebooks for data analysis or documentation. The ability to write arbitrary files to the filesystem can lead to unauthorized data modification or potential code execution if the written files are subsequently processed by other applications. This risk applies to any environment where users convert untrusted notebooks into other formats.

The vulnerability affects a wide range of versions, including those released years ago. Systems running nbconvert between version 5.4.0 and 7.17.1 are exposed to this attack vector. Because the exploit relies on the conversion process rather than executing the notebook code, it can bypass some standard safety controls that focus on cell execution.

What to watch

• Monitor for new versions of Jupyter nbconvert that address CVE-2026-114140.
• Check internal logs for unexpected file creation in sensitive directories during notebook conversion tasks.
• Verify that all instances of nbconvert are running version 7.17.2 or later to mitigate the risk.
• Review access controls for directories where converted notebook outputs are stored to limit potential damage.

Who needs to act first

Teams should prioritize updating systems that process notebooks from untrusted sources or external contributors. Before deploying the fix, administrators should test the update in a non-production environment to ensure compatibility with existing workflows. It is advisable to back up current configurations and notebook data before applying the patch. Organizations should also review their incident response plans to include procedures for detecting unauthorized file writes in output directories.

Background: CVSS score

The CVSS score explains vulnerability severity using a 0.0 to 10.0 scale. It measures attack vector, complexity, privileges required, and impact on confidentiality, integrity, and availability. You use this metric to prioritize patches, though you must adjust it for your specific environment to avoid wasting time on irrelevant threats.

Read the full guide: CVSS Score Explained: How to Read Risk Metrics and Prioritize Fixes

What to do and how to stay safe: Jupyter

• Audit your environment to identify all installations of Jupyter nbconvert and verify their current version numbers.
• Apply the update to version 7.17.2 as soon as possible to eliminate the path traversal vulnerability.
• Restrict the ability of users to convert notebooks from untrusted sources until the patch is deployed.
• Implement file integrity monitoring on directories used for notebook output to detect unauthorized changes.

Step-by-step guide: Virtual Patching Myths: What It Actually Fixes and Breaks

General security guidance from the Patch Gazette newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

Which versions of Jupyter nbconvert are affected by CVE-2026-114140?

Versions 5.4.0 through 7.17.1 are affected by this vulnerability.

Is there a fix available for this path traversal issue?

Yes, the issue is fixed in version 7.17.2 of Jupyter nbconvert.

What is the CVSS score for CVE-2026-114140?

The National Vulnerability Database rates the severity as high with a CVSS score of 8.8.