This paper presents a new generation of attacks against Microsoft Windows, and possibly other message-based windowing systems. The flaws presented in this paper are, at the time of writing, unfixable. The only reliable solution to these attacks requires functionality that is not present in Windows, as well as efforts on the part of every single Windows software vendor. Read more...

Applications within Windows are entirely controlled through the use of messages. When a key is pressed, a message is sent to the current active window which states that a key was pressed. When Windows decides that an application needs to redraw its client area, it send a message to the application. In fact, when any event takes place that an application needs to know about, it is sent a message. These messages are placed into a queue, and are processed in order by the application. This is a very reliable mechanism for controlling applications. However, on Win32 the mechanism for controlling these messages is flawed. Any application on a given desktop can send a message to any window on the same desktop, regardless of whether or not that window is owned by the sending application, and regardless of whether the target application wants to receive those messages. There is no mechanism for authenticating the source of a message; a message sent from a malicious application is indistinguishable from a message sent by the Windows kernel. It is this lack of authentication that we will be exploiting, taking into consideration that these messages can be used to manipulate windows and the processes that own them. The full background story