An issue was discovered in Special:MediaSearch in the MediaSearch extension in MediaWiki through 1.36.2. The suggestion text (a parameter to mediasearch-did-you-mean) was not being properly sanitized and allowed for the injection and execution of HTML and JavaScript via the intitle: search operator within the query.
https://phabricator.wikimedia.org/T291600
https://gerrit.wikimedia.org/r/q/If64eb5842237c92290d07ebc3fe14710d9de3fc2