This script is only used when RED is in DHCP mode and will be replaced by something else.
The new CGI directly replaces the old one. https://git.ipfire.org/?p=people/stevee/ipfire-2.x.git;a=commit;h=24d7c5ef6bea7b6521d309757d2fa0461935f89d
https://blog.ipfire.org/post/ipfire-2-25-core-update-141-release