The ScratchLogin extension through 1.1 for MediaWiki does not escape verification failure messages, which allows users with administrator privileges to perform cross-site scripting (XSS).

Authentication Bypass in Scratch Login (mediawiki-scratch-login)

in Scratch Login (MediaWiki extension) before version 1.1, any account can be logged into by using the same username with leading, trailing, or repeated underscore(s), since those are treated as whitespace and trimmed by MediaWiki. This affects all users on any wiki using this extension. Since version 1.1, comments by users whose usernames would be trimmed on MediaWiki are ignored when searching for the verification code.