There are quite a few MediaWiki extensions to prevent spam, and some extensions that let you delete pages //en masse//. What MediaWiki doesn't have yet is a capability to deal well with spam that's already in place on the wiki. The Nuke extension lets you do a mass deletion on all pages created by a single user or IP address, but that's not too helpful because spammers tend to switch quickly from one user/IP address to another, perhaps to get around such tools. (Also, Nuke only works on recent changes and has little filtering. T33858, T56208, T68447.) This planned extension would instead go through all the pages in the wiki, and use some logic to try to figure out which ones were spam pages; it would then display an interface to an administrator to be able to delete these pages - with a checkbox for each to let admins toggle the deletion of each one.
Identifying the spam pages should actually not be that difficult to do - from my experience, spam pages tend to be rather different from real wiki pages in content (almost complete lack of wikitext, other than external URLs), page history (created fully formed in a single edit), and so on.
Primary mentor: @Yaron_Koren
Other mentors: (optional, Phabricator username)
Estimated project time for a senior contributor: 2-3 weeks
Microtasks: T90637, T91092, T91222