WordPress Cookie Integrity Protection Privilege Escalation Vulnerability

A vulnerability has been identified in WordPress, which could be exploited by attackers to compromise an affected web site. This issue is caused by an error in the MAC calculation procedure when handling the "USERNAME" and "EXPIRY_TIME" parameters contained in the authentication cookie, which could be exploited by attackers to gain unauthorized administrative access (and execute arbitrary PHP code) by creating an account with a specially crafted username.