A spoofing vulnerability exists when an Office Web Apps server does not properly sanitize a specially crafted request. An authenticated attacker could exploit the vulnerability by sending a specially crafted request to an affected Office Web Apps server. The attacker who successfully exploited this vulnerability could then perform cross-site scripting attacks on affected systems and run script in the security context of the current user. For the vulnerability to be exploited, a user must click a specially crafted URL that takes the user to a targeted Office Web App site. In an email attack scenario, an attacker could exploit the vulnerability by sending an email message containing the specially crafted URL to the user of the targeted Office Web App site and convincing the user to click the specially crafted URL. The security update addresses the vulnerability by helping to ensure that Office Web AppsServer properly sanitizes web requests.