A concurrency bug in JupyterLab's PyPIExtensionManager.install() method causes the asynchronous is_install_allowed coroutine to never execute when install() is called directly, bypassing the extension allowlist/blocklist enforcement. This flaw affects versions >=4.6.0 <=4.6.1 and <=4.5.9. The vulnerability requires a specific deployment scenario involving direct calls to install() with untrusted input, configured allowlist/blocklist, enabled PyPI Extension Manager, and disabled or remote kernels/terminals. The standard HTTP API and UI are unaffected as they perform the check correctly. The issue is resolved in JupyterLab versions 4.6.2 and 4.5.10.

This vulnerability could allow unauthorized installation of extensions in affected JupyterLab deployments under specific conditions, potentially undermining configured allowlist/blocklist protections. However, the impact is limited as the default user interfaces and APIs are not affected, and exploitation requires direct invocation of the vulnerable method with untrusted input in a particular configuration. There is no confidentiality, integrity, or availability impact reported.

Upgrade to JupyterLab version 4.6.2 or later, or 4.5.10 or later, where this issue is fixed. If upgrading is not immediately possible, ensure that untrusted input cannot influence direct calls to PyPIExtensionManager.install(), and avoid disabling kernels and terminals or delegating them to remote hosts in affected deployments. Since the default HTTP API and Extension Manager UI are not vulnerable, using these interfaces mitigates risk.