When installing a package from a Mercurial VCS URL (ie "pip install
hg+...") with pip prior to v23.3, the specified Mercurial revision could
be used to inject arbitrary configuration options to the "hg clone"
call (ie "--config"). Controlling the Mercurial configuration can modify
how and which repository is installed. This vulnerability does not
affect users who aren't installing from Mercurial.
