Robert Paveza, a senior Web application developer with Web-based marketing company Terralever, has uncovered a two-step process for exploiting Windows Vista"s User Account Control. In his published paper, Paveza said that the vulnerability uses a two-part attack vector against a default Vista installation. The first step requires that a proxy infection tool be downloaded and run without elevation. That software can behave as the victim expects it to while it sets up a second malicious payload in the background. "For instance, if users believe they are downloading a "Pac-Man" clone, such a game could be run while the malicious software did its work in the background. This pattern of infection follows the typical Trojan horse model, piggybacking on what may be otherwise legitimate software," said Paveza.
Microsoft is aware of demonstrations that "purport" to show how a Vista system can be attacked. A Microsoft spokesperson said the demonstration provided by Paveza is of actions an attacker can take on a system that already has been compromised by another means: "With this in mind, it is important to note that user interaction is required for the initial infection of the Trojan to occur. The user must open the attacker"s malicious executable. Furthermore, the successive social engineering attempt will only be successful if the user inadvertently clicks on the malicious shortcut. In fact, at this point, the user must be part of the local administrator"s group or provide administrator credentials at the UAC prompt."