Copied /etc/init.d/lighttpd.webui from the image, but it looks like something else is also messed up:
root@LS-WXLBB0:~# /etc/init.d/lighttpd.webui
Terminated
root@LS-WXLBB0:~# /etc/init.d/lighttpd.webui start
2019-01-15 12:47:37: (server.c.614) No configuration available. Try using -f option.
root@LS-WXLBB0:~# /etc/init.d/lighttpd.webui start -f /etc/lighttpd/buffalo-web.conf
2019-01-15 12:48:18: (plugin.c.169) dlopen() failed for: /usr/lib/lighttpd/mod_indexfile.so /usr/lib/lighttpd/mod_indexfile.so: cannot open shared object file: No such file or directory
2019-01-15 12:48:18: (server.c.676) loading plugins finally failed
root@LS-WXLBB0:~# /etc/init.d/lighttpd.webui start -f /etc/lighttpd/lighttpd.conf
cat: can't open '/etc/melco/lighttpd.d/*.conf': No such file or directory
2019-01-15 12:48:49: (configfile.c.1248) base-docroot doesn't exist: /htdocs
2019-01-15 12:48:49: (server.c.646) setting default values failed
Still not willing to reinstall the firmware as long the actual SMB shares are functioning, but will try copying some more stuff from the image.