GFI HelpDesk before 4.99.9 contains a stored cross-site scripting vulnerability in the ticket subject field that allows authenticated staff members to inject malicious JavaScript by manipulating the editsubject POST parameter. Attackers can inject XSS payloads through inadequate sanitization in Controller_Ticket.EditSubmit() that bypass the incomplete SanitizeForXSS() method to execute arbitrary JavaScript when other staff members or administrators view the affected ticket.