The Internet Mail Connector (IMC) enables Microsoft Exchange Server to communicate with other mail servers via SMTP. When the IMC receives an SMTP extended Hello (EHLO) protocol command from a connecting SMTP server, it responds by sending a status reply that starts with the following:
250-Hello. A security vulnerability results because of an unchecked buffer in the IMC code that generates the response to the EHLO protocol command. If the total length of the message exceeds a particular value, the data would overrun the buffer. If the buffer were overrun with random data, it would result in the failure of the IMC. If, however, the buffer were overrun with carefully chosen data, it could be possible for the attacker to run code in the security context of the IMC, which runs as Exchange5.5 Service Account.
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