JupyterLab: Stored XSS in extension manager through package metadata unsanitized URI protocol
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.
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{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
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | jupyterlab | < 4.5.9 | 4.5.9 |
References
- https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-vmhf-c436-hxj4
- https://github.com/jupyterlab/jupyterlab/commit/4e61e07d0a91145b53fbf96ac74b0387f6bc51f6
- https://github.com/jupyterlab/jupyterlab/commit/d5d961f6e10a6442dddbf94d9a976b3897055a12
- https://github.com/jupyterlab/jupyterlab
- https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.9
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N- Weakness (CWE)
CWE-84- Platform
- Python (PyPI)
- Package
jupyterlab- Disclosed
- 19.06.2026
- Updated
- 14.10.2026 14:17
Sources and licenses
OSV / GitHub Advisory Database - GHSA-vmhf-c436-hxj4 - CC BY 4.0
Vulnerability history: jupyterlab
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 19
- First → latest
- 08.2021 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 8
- Medium 8
- Low 2
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 4
- 2025: 1
- 2026: 13
-
JupyterLab: Stored XSS in extension manager through package metadata unsanitized URI protocol this entry
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