An issue was discovered in MediaWiki before 1.35.7, 1.36.x and 1.37.x before 1.37.3, and 1.38.x before 1.38.1. XSS can occur in configurations that allow a JavaScript payload in a username. After account creation, when it sets the page title to "Welcome" followed by the username, the username is not escaped: SpecialCreateAccount::successfulAction() calls ::showSuccessPage() with a message as second parameter, and OutputPage::setPageTitle() uses text().

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.)

The WikibaseMediaInfo extension 1.35 for MediaWiki allows XSS because of improper template syntax within the PropertySuggestionsWidget template (in the templates/search/PropertySuggestionsWidget.mustache+dom file).

The MinervaNeue Skin in MediaWiki from 2019-11-05 to 2019-12-13 (1.35 and/or 1.34) mishandles certain HTML attributes, as demonstrated by IMG onmouseover= (impact is XSS) and IMG src=http (impact is disclosing the client's IP address). This can occur within a talk page topical header that is viewed within a mobile (MobileFrontend) context.

Mediawiki 1.31 before 1.31.1, 1.30.1, 1.29.3 and 1.27.5 contains an information disclosure flaw in the Special:Redirect/logid

Mediawiki 1.31 before 1.31.1, 1.30.1, 1.29.3 and 1.27.5 contains a flaw where contrary to the documentation, $wgRateLimits entry for 'user' overrides that for 'newbie'.

Mediawiki 1.31 before 1.31.1, 1.30.1, 1.29.3 and 1.27.5 contains a flaw where BotPasswords can bypass CentralAuth's account lock

Cross-site scripting (XSS) vulnerability in includes/actions/InfoAction.php in MediaWiki before 1.21.9 and 1.22.x before 1.22.6 allows remote attackers to inject arbitrary web script or HTML via the sort key in an info action.

Cross-site scripting (XSS) vulnerability in the outputPage function in includes/SkinTemplate.php in MediaWiki before 1.17.5, 1.18.x before 1.18.4, and 1.19.x before 1.19.1 allows remote attackers to inject arbitrary web script or HTML via the uselang parameter to index.php/Main_page.

includes/User.php in MediaWiki before 1.16.5, when wgBlockDisablesLogin is enabled, does not clear certain cached data after verification of an auth token fails, which allows remote attackers to bypass authentication by creating crafted wikiUserID and wikiUserName cookies, or by leveraging an unattended workstation.