"Its one that has plenty of people confused regarding what, exactly, it is," MacDonald said.
In fact, UAC isnt one capability; rather, its a set of Vista capabilities that collectively help to limit the ability of applications and users to make unsanctioned system changes—whether the user is running as an administrator or as a standard user.
"The idea is that when a piece of software is asking for user credentials … you shouldnt just hand them over," MacDonald said.
UACs raison dêtre is basically to cure the new operating system of a legacy of bad applications that freely granted administrator rights—a tendency that has eased malware writers jobs. "Malicious code would be far less effective if users ran without administrative privileges," MacDonald said.
Microsoft initially promoted UAC as a signifier of a new, more secure era for Windows. The security functions reputation was tarnished, however, when security researchers pointed out that UAC is vulnerable to social engineering attacks.
Microsoft confirmed that vulnerability, and defended UAC by describing it as a security feature rather than a hard security boundary such as a firewall.
The idea behind UAC is to limit user privileges as much as possible for most of a users interaction with the desktop. User rights are elevated only when necessary for administrative tasks, at which point a dialog box prompts the user to OK the escalation. Limiting normal permissions is a good thing, given that it limits the operating system surface an attacker can latch onto.
Aside from limiting the effectiveness of malicious code, the biggest impact of UAC, according to MacDonald, will be to change developer behavior so applications dont demand that users have to run as administrators to use them.
"[In the] longer term, [users should] require all application vendors to deliver applications that dont require administrative rights to run," he said.
No. 1 on the list of problems that organizations may face when implementing UAC is politics, MacDonald said, given that under UAC, tasks that have been classified as being administrative will require an administrators approval. The question an IT department should ask itself, he said, is if it is in fact able to restrict what users are allowed to do with their "personal" computers.
"Well-designed UAC implementations and applications wont prevent users from extending their work environments, but dont overlook the politics of exerting [total] control over the users computing environments," he said.
Another glitch could arise with applications in which redirection wont work; such applications arent supported by UAC.
It will also be difficult for standard users to install ActiveX controls and other browser extensions in Internet Explorer. Organizations will need to ensure that they have ways to dynamically modify whitelists or push down required browser extensions remotely or both, MacDonald said.
Finally, those deploying Vista should be aware that standard users can still install arbitrary software. "Its a common misconception [that] if you run everybody as a standard user they cant install standard applications," MacDonald said. As a result, application control may have to be supplied by third-party software.
MacDonald had additional advice on deploying UAC:
- Use the migration to Windows Vista as a catalyst to have more users run as "standard user." This may not be appropriate for all users, but can be for many.
- For administrators, require approval when an administrative task is attempted.
- When critical vulnerabilities are announced by Microsoft, see if the malicious code is restricted to running in the context of the user.
- Note that if the organizations goal is to "lock down" the computing environment, UAC wont be enough, and third-party tools will be required.