This security update resolves vulnerabilities in Microsoft Exchange Server. The most severe of the vulnerabilities could allow elevation of privilege if a user clicks a specially crafted URL that takes them to a targeted Outlook Web App site. An attacker would have no way to force users to visit a specially crafted website. Instead, an attacker would have to convince them to visit the website, typically by getting them to click a link in an instant messenger or email message that takes them to the attacker's website, and then convince them to click the specially crafted URL.