In MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4, XSS related to jQuery can occur. The attacker creates a message with [javascript:payload xss] and turns it into a jQuery object with mw.message().parse(). The expected result is that the jQuery object does not contain an <a> tag (or it does not have a href attribute, or it's empty, etc.). The actual result is that the object contains an <a href ="javascript... that executes when clicked.
An issue was discovered in MediaWiki 1.32.x through 1.34.x before 1.34.4. LogEventList::getFiltersDesc is insecurely using message text to build options names for an HTML multi-select field. The relevant code should use escaped() instead of text().
An issue was discovered in the OATHAuth extension in MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4. For Wikis using OATHAuth on a farm/cluster (such as via CentralAuth), rate limiting of OATH tokens is only done on a single site level. Thus, multiple requests can be made across many wikis/sites concurrently.
An issue was discovered in MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4. The non-jqueryMsg version of mw.message().parse() doesn't escape HTML. This affects both message contents (which are generally safe) and the parameters (which can be based on user input). (When jqueryMsg is loaded, it correctly accepts only whitelisted tags in message contents, and escapes all parameters. Situations with an unloaded jqueryMsg are rare in practice, but can for example occur for Special:SpecialPages on a wiki with no extensions installed.)
An information leak was discovered in MediaWiki before 1.31.10 and 1.32.x through 1.34.x before 1.34.4. Handling of actor ID does not necessarily use the correct database or correct wiki.
In MediaWiki before 1.31.8, 1.32.x and 1.33.x before 1.33.4, and 1.34.x before 1.34.2, private wikis behind a caching server using the img_auth.php image authorization security feature may have had their files cached publicly, so any unauthorized user could view them. This occurs because Cache-Control and Vary headers were mishandled.
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.