Per https://wikiapiary.com/wiki/Generator:Generators more than 96% of MediaWiki website are using a MediaWiki version that is no longer supported. Old MediaWiki versions clearly have security issues.

Ideas include:

• Display a message in Special:Version that clearly states the MediaWiki version is no longer supported
• Display a message when running a maintaince script and sysadmins must press Enter to continue

(feel free to create subtasks for specific ideas)