MediaWiki through 1.32.1 has Incorrect Access Control (issue 1 of 3). A spammer can use Special:ChangeEmail to send out spam with no rate limiting or ability to block them. Fixed in 1.32.2, 1.31.2, 1.30.2 and 1.27.6.
Mediawiki before 1.28.1 / 1.27.2 / 1.23.16 contains a flaw were Spam blacklist is ineffective on encoded URLs inside file inclusion syntax's link parameter.