ImportDump is an extension for mediawiki designed to automate user import requests. Anyone who can edit the interface strings of a wiki (typically administrators and interface admins) can embed XSS payloads in the messages for dates, and thus XSS anyone who views Special:RequestImportQueue. This issue has been patched in commit `d054b95` and all users are advised to apply this commit to their branch. Users unable to upgrade may either Prevent access to Special:RequestImportQueue on all wikis, except for the global wiki; and If an interface administrator (or equivalent) level protection is available (which is not provided by default) on the global wiki, protect the affected messages up to that level. This causes the XSS to be virtually useless as users with those rights can already edit Javascript pages. Or Prevent access to Special:RequestImportQueue altogether.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.