# CVE-2026-67338: JupyterLab stored cross-site scripting in Extension Manager

Source: https://junglewise.ai/threats/cve-2026-67338-jupyterlab-stored-cross-site-scripting-in-extension-manager  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-01. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-67338 · Severity: medium · CVSS 6.1 · Published 2026-08-01

JupyterLab's Extension Manager is a feature that allows users to discover and install extensions to enhance the notebook environment. A vulnerability in the Extension Manager fails to validate protocol types in package metadata URLs, allowing an attacker to publish a malicious PyPI package with JavaScript execution code embedded in the project metadata. When a user clicks on the extension name, arbitrary JavaScript executes in the JupyterLab application context, potentially leading to credential theft, data exfiltration, or unauthorized actions.

Technologies: [jupyterlab (PyPI)](https://junglewise.ai/threats/technologies/pypi-jupyterlab). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-67338 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-67338 being exploited in the wild.

**How severe is CVE-2026-67338?** Medium severity, with a CVSS score of 6.1, published 1 August 2026.

**Which products and versions are affected?** jupyterlab (PyPI) ECOSYSTEM:introduced=0,fixed=4.5.9.

**Is there a fix for CVE-2026-67338?** Yes. jupyterlab (PyPI): upgrade to 4.5.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-67338 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-67338?** Check whether you run jupyterlab (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- jupyterlab (PyPI): upgrade to 4.5.9 or later

  ```sh
  pip install "jupyterlab>=4.5.9"
  ```


## Technical details

This is a stored cross-site scripting (XSS) vulnerability in JupyterLab's Extension Manager component, specifically in the `homepage_url` field handling within package metadata. The vulnerability arises from insufficient URI protocol validation when rendering extension names as clickable links. An attacker can publish a malicious PyPI package with a `javascript:` URL in the project metadata; when a JupyterLab user clicks the extension name link, the JavaScript URL executes in the JupyterLab origin context. No user authentication is required; exploitation requires that a user install and view a malicious extension in the Extension Manager. The fix restricts allowed URL protocols (e.g., to http/https only) and forbids relative URLs to prevent JavaScript protocol execution. Patches are available in JupyterLab 4.5.9 and later.

## Affected products

- JupyterLab JupyterLab before 4.5.9

## Identifiers

- CVE-2026-67338
- GHSA-vmhf-c436-hxj4

## Timeline

- 2026-08-01: disclosed
- 2026: patched: Fix released in JupyterLab 4.5.9

## References

- [https://github.com/jupyterlab/jupyterlab/commit/4e61e07d0a91145b53fbf96ac74b0387f6bc51f6](https://github.com/jupyterlab/jupyterlab/commit/4e61e07d0a91145b53fbf96ac74b0387f6bc51f6)
- [https://github.com/jupyterlab/jupyterlab/commit/d5d961f6e10a6442dddbf94d9a976b3897055a12](https://github.com/jupyterlab/jupyterlab/commit/d5d961f6e10a6442dddbf94d9a976b3897055a12)

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