Mediawiki before 1.28.1 / 1.27.2 / 1.23.16 has a flaw where Special:UserLogin?returnto=interwiki:foo will redirect to external sites.
{ "binaries": [ { "binary_version": "1:1.27.4-3", "binary_name": "mediawiki" }, { "binary_version": "1:1.27.4-3", "binary_name": "mediawiki-classes" } ], "availability": "No subscription required" }