GFI MailEssentials AI < 22.4 Advanced Content Filtering Rule Stored XSS

GFI MailEssentials AI versions prior to 22.4 contain a stored cross-site scripting vulnerability in the Advanced Content Filtering rule creation workflow. An authenticated user can supply HTML/JavaScript in the ctl00$ContentPlaceHolder1$pv1$txtRuleName parameter to /MailEssentials/pages/MailSecurity/advancedfiltering.aspx, which is stored and later rendered in the management interface, allowing script execution in the context of a logged-in user.