CVE-2026-67338

JupyterLab before 4.5.9 contains a stored cross-site scripting vulnerability in the Extension Manager that fails to validate URI protocols in package metadata URLs. Attackers can publish malicious PyPI packages with javascript: URLs in project metadata that execute arbitrary JavaScript in the JupyterLab origin when users click the extension name.

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

Patched in 4.5.9, commits 4e61e07 and d5d961f

JupyterLab is the next-generation user interface for Project Jupyter offering all the familiar building blocks of the classic Jupyter Notebook (notebook, terminal, text editor, file browser, rich outputs, etc.) in a flexible and powerful user interface.

Security Fix(es):

JupyterLab before 4.5.9 contains a stored cross-site scripting vulnerability in the Extension Manager that fails to validate URI protocols in package metadata URLs. Attackers can publish malicious PyPI packages with javascript: URLs in project metadata that execute arbitrary JavaScript in the JupyterLab origin when users click the extension name.(CVE-2026-67338)

JupyterLab versions >=4.6.0,<=4.6.1 and <=4.5.9 contain an allowlist/blocklist enforcement gap in PyPIExtensionManager.install(). A missing 'await' caused the is_install_allowed coroutine to never execute, so the extension allowlist/blocklist check was not enforced for direct callers of install(). The stock JupyterLab HTTP API and Extension Manager UI are not affected, as they perform a separate, correctly awaited check. The issue affects only deployments where a custom extension or downstream integration imports PyPIExtensionManager and calls install() directly with a package name influenced by untrusted input, an allowlist/blocklist is configured, the PyPI Extension Manager is enabled, and kernels and terminals are disabled or delegated to remote hosts. Fixed in JupyterLab 4.6.2 and 4.5.10.(CVE-2026-73626)

JupyterLab before 4.5.9 contains a stored cross-site scripting vulnerability in the Extension Manager that fails to validate URI protocols in package metadata URLs. Attackers can publish malicious PyPI packages with javascript: URLs in project metadata that execute arbitrary JavaScript in the JupyterLab origin when users click the extension name.

JupyterLab before 4.5.9 contains a stored cross-site scripting vulnerability in the Extension Manager that fails to validate URI protocols in package metadata URLs. Attackers can publish malicious PyPI packages with javascript: URLs in project metadata that execute arbitrary JavaScript in the JupyterLab origin when users click the extension name.