Fewer Permissions Are Key to Longhorn Security

Software engineers who attend Microsoft's annual Windows Hardware Engineering Conference later this month could get their first taste of a new Windows user permissions model that could change the way thousands of programs are developed and run. But as the company prepares for the final Longhorn development push, questions remain about its plans for a new user privileges model called Least-Privilege User Account, or LUA.

Network administrators enforce strict user privileges on networks and restrict access to servers and other resources, but individual Windows users often log on to their Windows system as a local administrator because of the difficulty of running even common programs with just user permissions. Authors of viruses, worms, bots, and spyware take advantage of those elevated privileges to install malicious programs and change the configuration of Windows to keep their creations from being detected, shut down, or removed, experts say.

Microsoft claims that LUA will make life tougher for hackers and virus writers by limiting access to administrator permissions on Windows systems. But the company has been mum in recent months about its plans for implementing LUA in Longhorn, and it is considering incentives to encourage adoption of LUA (pronounced "loo-ah") by skeptical independent software vendors, including a new logo program for LUA compliance, according to interviews with independent software vendors and industry experts.

Least permissions is a principle of computer security that recommends giving software applications and their users no more privileges on an operating system than are absolutely necessary. Widely accepted within the software development community, least permissions has often been overlooked in recent years as operating system and application software companies have worked to make using software easier, says John Pescatore, vice president of Internet security at research firm Gartner.

Least Is Best

Microsoft says it will encourage the use of least permissions in Longhorn by making it easier for users to do common tasks without administrator privileges. For example, the company may modify Windows so reduced-permissions users can alter display and power-management settings on their machine and use VPN (virtual private network) technology more easily. Other changes will allow developers to create per-user installations of applications, with user-specific settings saved in the My Programs folder, rather than a globally accessible program files directory that requires administrative permissions to change, according to documents and presentations on Microsoft's Web page.

Microsoft also proposes application manifests, which allow developers to define the permissions an application needs to operate properly and can be signed by independent software vendors to ensure integrity. Deployment manifests, signed by IT departments, will allow network administrators to dictate how much trust an application should have on the network, according to the documents.

The changes are intended to revive an important security concept that has been a low priority among many Windows users and application developers.

"I don't think the notion of application runtime permissions are either well understood or well handled," said Jason Rimmer, chief architect at Vertex Inc., a tax technology and services provider based in Berwyn, Pennsylvania. "Coming from Unix, you're used to asking 'Does this run under root or not?' But Windows operators have never had to consider that. LUA will force that choice on people," he said.

Administrator Needed?

For example, Windows programs commonly save user-specific files to critical areas of the operating system, such as the program files directory or protected parts of the Windows Registry, which stores configuration information and is off-limits to regular users, wrote Keith Brown, cofounder of Pluralsight, in April 2004.

Application developers who log on to their development machines as administrators when they write code create programs that assume that level of privilege but have trouble when run by a user with reduced permissions, according to Brown's work, which estimated that 90 percent of Windows software can't be installed without administrator access to Windows, and that 70 percent won't run properly unless the user is an administrator.

A strictly enforced LUA model could make it harder for worms and viruses to take over Windows systems. But Microsoft may have a tough time changing user and developer behavior, even with new features that support the LUA regime in Longhorn, experts warn.

"The [LUA] framework we're talking about has been there for ten years.... The fact is that vendors go the lazy route and continue to dump program settings in [the program files directory]. Software vendors, including Microsoft, have to stop writing lazy code," says Brian Bergin, president of Terabyte Computers in Boone, North Carolina.

Making It Easier

To encourage adoption of LUA features and principles, Microsoft has been working closely with Macrovision to develop application installation and setup programs for use with Longhorn that incorporate LUA concepts, says Bob Corrigan, product manager for the InstallShield product at Macrovision.

Installations are a pain point for LUA in Windows, because they require files to be written to different areas of the Windows file system and configuration changes in the Windows Registry that often are inaccessible to ordinary user accounts.

"The advent of LUA will compel [independent software vendors] and corporations to take a close look at what applications do at the point they're [installed]," Corrigan says.

Macrovision hopes to simplify some of the complexity of LUA in its applications. For example, future versions of InstallShield will allow independent software vendors to build application installation and setup programs that segregate user and administrator functions so that users don't have to have administrative access to install some software and that administrative-level permissions aren't accidentally extended to non-administrators, he says.

That's a change from current Windows installation routines, which typically mash together common and administrative components during installation without any clear distinction between the two, Corrigan says.

Microsoft is also weighing a logo program, akin to the Windows logo program, that will grant special status to applications that comply with LUA principles, he says.

Microsoft declined repeated invitations to discuss LUA's role in upcoming Longhorn releases, but says it is considering LUA for future releases as part of an overall vision for multilayered security known as "defense in depth," according to an e-mail statement attributed to Amy Roberts, director of the Security Business and Technology Unit at Microsoft.

Some aspects of LUA may also be tied to the next-generation Windows File System, which Microsoft said in August that it will not ship with the first version of Longhorn at the end of 2006, Pescatore says.

Regardless, LUA will be a major change for many application developers, and Microsoft needs to begin laying the groundwork for the change, experts agree.