https://security-tracker.debian.org/tracker/DSA-5901-1
An issue was discovered in the CheckUser extension through 1.34 for MediaWiki. Certain sensitive information within oversighted edit summaries made available via the MediaWiki API was potentially visible to users with various levels of access to this extension. Said users should not have been able to view these oversighted edit summaries via the MediaWiki API.
resources/src/mediawiki.page.ready/ready.js in MediaWiki before 1.35 allows remote attackers to force a logout and external redirection via HTML content in a MediaWiki page.
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.