An email filter bypass exists in the way that Microsoft Exchange parses HTML messages that could allow information disclosure. An attacker who successfully exploited the vulnerability could identify, fingerprint, and track a user online if the user views email messages using Outlook Web Access (OWA). An attacker could also combine this vulnerability with another one, such as a Cross-Site Request Forgery (CSRF), to amplify the attack.
To exploit the vulnerability, an attacker could include specially crafted image URLs in OWA messages that could be loaded, without warning or filtering, from the attacker-controlled URL. This callback vector provides an information disclosure tactic used in web beacons and other types of tracking systems. The update corrects the way that Exchange parses HTML messages.

Further information on this exploit is available at : MS16-079