A vulnerability exists because the ListBox control and the ComboBox control both call a function, which is located in the User32.dll file, that contains a buffer overrun. An attacker who had the ability to log on to a system interactively could run a program that could send a specially-crafted Windows message to any applications that have implemented the ListBox control or the ComboBox control, causing the application to take any action an attacker specified. An attacker must have valid logon credentials to exploit the vulnerability. This vulnerability could not be exploited remotely.

see http://www.microsoft.com/technet/security/bulletin/ms03-045.mspx