MsUpload: Stored Cross-Site Scripting (XSS) via unsanitized msu-continue system message

The MsUpload extension for MediaWiki is vulnerable to stored XSS via the msu-continue system message, which is inserted into the DOM without proper sanitization. The vulnerability occurs in the file upload UI when the same filename is uploaded twice. This issue affects Mediawiki - MsUpload extension: from 1.39.X before 1.39.13, from 1.42.X before 1.42.7, from 1.43.X before 1.43.2.