In MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4, Special:UserRights exposes the existence of hidden users.
{ "binaries": [ { "binary_version": "1:1.27.4-3", "binary_name": "mediawiki" }, { "binary_version": "1:1.27.4-3", "binary_name": "mediawiki-classes" } ] }
{ "binaries": [ { "binary_version": "1:1.31.7-1", "binary_name": "mediawiki" }, { "binary_version": "1:1.31.7-1", "binary_name": "mediawiki-classes" } ] }