This executable can spawn an interactive system shell.
This function can be performed by any unprivileged user.
plymouth ask-for-password --prompt=x --command=/bin/sh
This function is performed by the privileged user if executed via sudo because the acquired privileges are not dropped.
plymouth ask-for-password --prompt=x --command=/bin/sh
This function is performed by the privileged user if the executable has the SUID bit set and the right ownership because the effective privileges are not dropped.
plymouth ask-for-password --prompt=x --command='/bin/sh -p'