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.
An issue was discovered in the ProofreadPage (aka Proofread Page) extension for MediaWiki through 1.39.3. In includes/Page/PageContentHandler.php and includes/Page/PageDisplayHandler.php, hidden users can be exposed via public interfaces.
An issue was discovered in the Cargo extension for MediaWiki through 1.39.3. XSS can occur in Special:CargoQuery via a crafted page item when using the default format.
An issue was discovered in the CheckUser extension for MediaWiki through 1.39.3. In Special:CheckUser, a check of the "get edits" type is vulnerable to HTML injection through the User-Agent HTTP request header.
An issue was discovered in the Cargo extension for MediaWiki through 1.39.3. It allows one to store javascript: URLs in URL fields, and automatically links these URLs.
An issue was discovered in the GoogleAnalyticsMetrics extension for MediaWiki through 1.39.3. The googleanalyticstrackurl parser function does not properly escape JavaScript in the onclick handler and does not prevent use of javascript: URLs.
An issue was discovered in MediaWiki before 1.35.11, 1.36.x through 1.38.x before 1.38.7, and 1.39.x before 1.39.4. BlockLogFormatter.php in BlockLogFormatter allows XSS in the partial blocks feature.
An issue was discovered in MediaWiki before 1.35.8, 1.36.x and 1.37.x before 1.37.5, and 1.38.x before 1.38.3. Upon an action=rollback operation, the alreadyrolled message can leak a user name (when the user has been revision deleted/suppressed).