The core Upload module in Drupal 4.7.x before 4.7.8 and 5.x before 5.3 places the .html extension on a whitelist, which allows remote attackers to conduct cross-site scripting (XSS) attacks by uploading .html files.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.008
EPSS Ranking 72.5%