Manual:$wgProxyList

Details
Sets a list of IP addresses to be banned. (Originally meant for presumed open proxies that would most likely only be used for vandalism and block evasion, but can be used for blocking any kind of unwanted actors.)

This can be an array of IP addresses or a string with the path to a file with each IP address on a separate line.

From an interface message
Copy and paste a comma-delimited list (e.g. 1.0.170.183,1.0.170.188,1.0.170.234,1.0.170.24) of open proxies into "MediaWiki:Openproxylist"; then put the following in :