This bulletin covers four vulnerabilities in Microsoft Exchange Server. The most critical issue is a heap overflow that occurs when decoding Base 64 encoded MIME attachments. To exploit this vulnerability, an attacker would direct a specially-crafted email to a victim user. The user would have to view the email through the Outlook Web Access, IMAP, or POP3 interface in order for the exploit to work. Users reading mail through MAPI interfaces cannot trigger this exploit. Once the exploit is triggered, the attacker has complete control over the Exchange server. This vulnerability is challenging to locate, but we would not be surprised to see exploit POCs circulating not long after public disclosure. The second vulnerability allows an attacker to execute web scripts within the context of Outlook Web Access when a user views a specially crafted HTML email. This attack is similar to a cross-site scripting attack. Its most common application is likely to be theft of the victim's access credentials for the Outlook Web Server. The other two vulnerabilities are denial of service issues. An attacker with unauthenticated access to the Exchange IMAP Server could crash the server by sending a malformed string literal. Attackers could also crash Exchange by sending an email with a malformed iCal file to any user on the server.