---
id: GHSA-vmhf-c436-hxj4
title: >-
  JupyterLab: Stored XSS in extension manager through package metadata
  unsanitized URI protocol
summary: >-
  JupyterLab: Stored XSS in extension manager through package metadata
  unsanitized URI protocol
severity: medium
cwe:
  - CWE-84
vendor: jupyterlab
product: jupyterlab
affected:
  - jupyterlab <= 4.5.8
patched:
  - jupyterlab 4.5.9
published: '2026-06-19'
updated: '2026-06-19'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-vmhf-c436-hxj4'
references:
  - url: >-
      https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-vmhf-c436-hxj4
  - url: >-
      https://github.com/jupyterlab/jupyterlab/commit/4e61e07d0a91145b53fbf96ac74b0387f6bc51f6
  - url: >-
      https://github.com/jupyterlab/jupyterlab/commit/d5d961f6e10a6442dddbf94d9a976b3897055a12
  - url: 'https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.9'
  - url: 'https://github.com/advisories/GHSA-vmhf-c436-hxj4'
tags:
  - ghsa
  - pip
ingestedAt: '2026-06-22T15:52:21.099Z'
ecosystem: pip
---

## Overview

A malicious PyPI package can place a `javascript:` URL in its `[project.urls]` metadata. JupyterLab's Extension Manager renders this as the extension's home-page link without validating the protocol, so a user who clicks the extension name executes attacker-controlled JavaScript in the JupyterLab origin.

### Details

One of the PyPI package's URL (jupyterlab/extensions/pypi.py) is copied straight into the `homepage_url` rendered by the frontend in packages/extensionmanager/src/widget.tsx#L77-L88.

```python
best_guess_home_url = (
    homepage_url            # home_page / [project.urls] Homepage
    or data.get("project_url")
    or data.get("package_url")
    or documentation_url    # docs_url / [project.urls] Documentation
    or source_url           # [project.urls] Source Code
    or bug_tracker_url      # bugtrack_url / [project.urls] Bug Tracker
)

# homepage_url=best_guess_home_url
```

```tsx
{entry.homepage_url ? (
  <a href={entry.homepage_url} target="_blank" rel="noopener noreferrer" ...>
    {entry.name}
  </a>
) : ( <div>{entry.name}</div> )}
```

### Impact

An attacker needs to publish a package to PyPI (no access to the target). When the package appears in a victim's extension manager list and the victim clicks the extension name, the payload runs in the JupyterLab origin.

Preconditions: Extension Manager enabled with the default PyPI source, the malicious package appears in the victim's list/search results.

### Patches
Patched in [4.5.9](https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.9), commits [4e61e07](https://github.com/jupyterlab/jupyterlab/commit/4e61e07d0a91145b53fbf96ac74b0387f6bc51f6) and [d5d961f](https://github.com/jupyterlab/jupyterlab/commit/d5d961f6e10a6442dddbf94d9a976b3897055a12)

## Affected packages

- `jupyterlab <= 4.5.8`

## Remediation

Upgrade to a patched release:

- `jupyterlab 4.5.9`