An XSS issue was discovered in OpenSlides before 4.2.5. When submitting descriptions such as Moderator Notes or Agenda Topics, an editor is shown that allows one to format the submitted text. This allows insertion of various HTML elements. When trying to insert a SCRIPT element, it is properly encoded when reflected; however, adding attributes to links is possible, which allows the injection of JavaScript via the onmouseover attribute and others. When a user moves the mouse over such a prepared link, JavaScript is executed in that user's session.