Unfortunately, UAC is not perfect. On her blog, Joanna Rutkowska details several flaws in Vista's UAC implementation that are potentially exploitable. For example, software installers are always allowed to run with full administrative privilege, just like in old-fashioned Windows. In addition, Symantec security analyst Ollie Whitehouse points out that Vista ships with executables that can be used to compromise UAC.

“I still think that Microsoft did a good job with Vista,” Rutkowska says, yet the significance of these discoveries is clear: Don’t expect UAC to eliminate problems associated with the administrator account overnight.

Programmatic exploits aren’t the only way around UAC’s protections, either. User behavior is equally critical. UAC confirmation dialogs can be intrusive and somewhat cryptic. Users might be tempted to simply disable UAC out of frustration, or they might become so numb to the UAC warning messages that they click “OK” without thinking. What’s more, they can easily be tricked into doing the wrong thing using social engineering or deception.

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“Windows Vista provides many features to protect your system, but they require proper use,” reads Microsoft’s Windows Vista Security Best Practice Guidance for Consumers on the subject of UAC. “Your system security is only as strong as your actions, so think before you click.” In other words, relying on UAC puts the responsibility for system security in the hands of the individual user — hardly an ideal scenario.

In fact, Microsoft discourages customers from thinking of UAC as an explicit security boundary — and therefore, as Rutkowska notes, it does not consider flaws in the UAC implementation to be security flaws. Don’t ignore this point. It speaks volumes to how IT should view UAC within the enterprise environment.

Tweaking out
Microsoft has added numerous other features to Windows Vista besides UAC, many of which are intended to increase the overall security of the OS. But upon closer examination these add-ons are only marginal improvements over previous versions of Windows.

Windows Firewall has been enabled by default on all new Windows installs since the introduction of Windows XP Service Pack 2. With Vista, Windows Firewall gains the capability of blocking outgoing connections as well as incoming ones — a marked improvement, when you consider the growing threats of spyware, phishing, and DDoS attacks. Unfortunately, the filtering of outgoing packets is not enabled by default. In other words, Vista’s firewall won’t provide significantly more protection than the one included in XP SP2 without manual configuration.