The mediawiki manual for spam prevention contains instructions for downloading from stopforumspam's huge list. The particular site provides CIDR ranges as well as huge lists of IPs, and the documentation appears to perfer the raw IP list.

This is, obviously, caused by $wgProxyList being documented as a list of IP addresses. But does it always have to be a list of only IP addresses? At least in MediaWiki core, User.php preprocesses the list with IPSet, which does accept CIDR ranges. Using the CIDR ranges would mean a smaller list in general, and it would certainly be a great thing if the configuration allowed them formally.

(I am not sure how this will affect extensions -- logically they won't try to match against a huge list on their own without some libraries, right?)