Interpretation conflict in Drupal 4.7.x before 4.7.11 and 5.x before 5.6, when Internet Explorer 6 is used, allows remote attackers to conduct cross-site scripting (XSS) attacks via invalid UTF-8 byte sequences, which are not processed as UTF-8 by Drupal's HTML filtering, but are processed as UTF-8 by Internet Explorer, effectively removing characters from the document and defeating the HTML protection mechanism.