@phnt

> I could find exactly one reason for it.

Actually, it was just lazy admin shit: it was connected to a URL, but the fastcgi user didn't have permission to talk to the nginx socket, and their solution was to make a SUID binary that the PHP script could call. This was probably exposed somewhere through some UI thing but they also used it for stuff like triggering a rebuild:
sync-git.sh
imgboard.php