A denial of service vulnerability exists in Windows when the Internet Protocol Security (IPSec) service improperly handles encryption negotiation. An attacker who successfully exploited the vulnerability could cause the system to become nonresponsive.
To exploit this vulnerability an attacker must have valid credentials. An attacker could exploit this vulnerability by using a malicious application to connect to a target machine and cause the server to become nonresponsive. The update addresses the vulnerability by adding an additional check to verify encryption negotiation.

Further information on this exploit is available at : MS15-120