An issue was discovered in includes/specials/SpecialMovePage.php in MediaWiki before 1.39.7, 1.40.x before 1.40.3, and 1.41.x before 1.41.1. If a user with the necessary rights to move the page opens Special:MovePage for a page with tens of thousands of subpages, then the page will exceed the maximum request time, leading to a denial of service.
An issue was discovered in includes/CommentFormatter/CommentParser.php in MediaWiki before 1.39.7, 1.40.x before 1.40.3, and 1.41.x before 1.41.1. XSS can occur because of mishandling of the 0x1b character, as demonstrated by Special:RecentChanges#%1b0000000.
An issue was discovered in the Phonos extension in MediaWiki before 1.40.2. PhonosButton.js allows i18n-based XSS via the phonos-purge-needed-error message.
An issue was discovered in the GlobalBlocking extension in MediaWiki before 1.40.2. For a Special:GlobalBlock?uselang=x-xss URI, i18n-based XSS can occur via the parentheses message. This affects subtitle links in buildSubtitleLinks.
An issue was discovered in the CheckUserLog API in the CheckUser extension for MediaWiki through 1.39.3. There is incorrect access control for visibility of hidden users.
An issue was discovered in SubmitEntityAction in Wikibase in MediaWiki through 1.39.3. Because it doesn't use EditEntity for undo and restore, the intended interaction with AbuseFilter does not occur.
An issue was discovered in SiteLinksView.php in Wikibase in MediaWiki through 1.39.3. There is XSS via a crafted badge title attribute. This is also related to lack of escaping in wbTemplate (from resources/wikibase/templates.js) for quotes (which can be in a title attribute).
An issue was discovered in the CheckUser extension for MediaWiki through 1.39.3. In certain situations, an attempt to block a user fails after a temporary browser hang and a DBQueryDisconnectedError error message.