iDefense Security Advisory 02.13.07 - Remote exploitation of a design error in Microsoft Corp.'s 'wininet.dll' FTP client code could allow an attacker to execute arbitrary code. The vulnerability specifically exists in the parsing of reply lines from remote FTP servers. During an FTP session, the client makes requests for the server to perform some operation and the server responds with a numeric code, a human readable message and possibly some other information. As there can be multiple lines in a reply, code in the client breaks the reply up into lines, putting a null byte (character 0x00) after any end of line character. In the case where a line ends exactly on the last character of the reply buffer, the terminating null byte is written outside of the allocated space, overwriting a byte of the heap management structure. By sending a specially crafted series of replys to the client, the heap may be corrupted in a controlled way to cause the execution of arbitrary code.
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