GHSA-89vp-jrxv-24w8: JupyterLab: PyPI extension blocklist package-name canonicalization bypass

JupyterLab’s PyPI extension manager enforces blocked_extensions_uris by comparing the requested install name to blocklist entries with a custom string normalization that is weaker than PyPI package-name canonicalization. An authenticated user can request a PyPI-equivalent spelling such as JupyterLab.Git for a blocklisted package such as jupyterlab-git; JupyterLab accepts the install request even though pip resolves the variant to the same package.

This has security implications only for deployments that combine all of the following:

• an allowlist/blocklist configured with the intent of restricting which packages users can install;
• the (default) PyPI Extension Manager enabled; and
• kernels and terminals disabled or delegated to remote hosts (otherwise a user with kernel access can install packages directly regardless of this check)