Hacker finds way to run desktop applications on Windows RT

The method exploits a kernel vulnerability to bypass the restriction Microsoft built into Windows RT, the hacker said

A hacker claims to have found a method of bypassing the code integrity mechanism in Windows RT, therefore allowing for desktop-style programs to be installed on the platform.

The hacker, who uses the online moniker "clrokr", documented the bypass method in a blog post on Sunday.

Windows RT is a special version of Microsoft Windows designed for lightweight PCs and tablets that are based on the ARM architecture, including Microsoft's Surface tablet. Compared to Windows 8, Windows RT only allows Metro apps downloaded from the Windows Store to be installed. These applications are designed only for the Metro interface and don't have access to the regular Windows desktop.

That said, Windows RT does come with a few preinstalled desktop-enabled applications, like Microsoft Office RT, a special version of Microsoft Office 2013, and Internet Explorer 10.

According to clrokr, the restriction of installing only Metro-style apps on Windows RT is enforced through a code integrity mechanism that checks the application's signature before allowing it to be installed. This prevents users from simply taking a desktop application compiled for the ARM architecture and installing it on their Windows RT devices.

"Deep in the kernel, in a hashed and signed data section protected by UEFI's Secure Boot, lies a byte that represents the minimum signing level," clrokr said. "The minimum signing level determines how good an executable's signature is on a scale like this: Unsigned(0), Authenticode(4), Microsoft(8), Windows(12). The default value on x86 machines [Windows 8 and previous versions] is of course 0 because you can run anything you like on your computer. On ARM machines, it defaults to 8."

The minimum signing level enforced by Windows RT can be changed by exploiting a vulnerability in the Windows kernel that had existed for some time and is also present in Windows RT, in order to modify that special byte in memory, clrokr said.

The hacker decided to disclose the bypass method publicly because he feels that Microsoft's decision to artificially ban traditional desktop applications on the platform is a bad marketing move that decreases the value of Windows RT devices.

"Windows RT needs the Win32 ecosystem to strengthen its position as a productivity tool," he said. "There are enough 'consumption' tablets already."

"The reason I tried to disable Code Integrity has nothing to do with Win32 or WinRT," he said in a discussion thread on Reddit. "It has to do with choice. Microsoft wants devs to go through the [Windows] Store and it is understandable from a money standpoint. But allowing Win32 apps could have helped the chicken-and-egg problem the Surface is going to die from."

Clrokr doesn't agree with the argument that traditional desktop applications require more resources and consume more battery power than Metro-style apps, which might have led to Microsoft's decision to ban them in Windows RT.

"This is not quite true," he said. "It all really depends on the quality of the programs. Win32 and WinRT apps are not as different as you might think. You can easily build a crappy, slow, unresponsive WinRT app. And there is no reason to believe that Win32 apps have higher requirements when it comes to processing power and memory."

It's not clear how Microsoft will react to the public availability of this bypass method. The company did not immediately respond to a request for comment sent Monday.

The hack does have some limitations. For one, the signing-level byte cannot be permanently changed because of the Secure Boot feature that checks the integrity of the OS after every reboot and reverts unauthorized changes.

This means that the bypass procedure must be performed after every reboot. Tablet devices are not rebooted that often, so this is not necessarily a huge inconvenience, but it does mean that the use of the hack is, at least for now, restricted to more technical users.

Another limitation is that x86 desktop programs can't simply be installed on Windows RT; they need to be recompiled for the ARM architecture. For open-source programs this might prove easier to do, but for closed-source ones the only way to do it is to convince the original developers to create versions for ARM.

In a discussion thread on the XDA-Developers forums, a user claims to have already compiled PuTTY -- an open-source SSH, Telnet and rlogin client application -- for ARM and successfully installed it on a Surface Tablet using clrokr's hack.

In the same thread someone suggested the idea of porting Chromium, the open-source browser that serves as the basis for Google Chrome, to ARM and installing it on Microsoft Surface. Clokr also said on Reddit that he has seen 7-Zip running on Windows RT.

Join the newsletter!

Error: Please check your email address.
Rocket to Success - Your 10 Tips for Smarter ERP System Selection

Tags MicrosoftsecurityWindowsAccess control and authenticationsoftwaremobileoperating systemsExploits / vulnerabilities

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Cool Tech

Breitling Superocean Heritage Chronographe 44

Learn more >

SanDisk MicroSDXC™ for Nintendo® Switch™

Learn more >

Toys for Boys

Family Friendly

Panasonic 4K UHD Blu-Ray Player and Full HD Recorder with Netflix - UBT1GL-K

Learn more >

Stocking Stuffer

Razer DeathAdder Expert Ergonomic Gaming Mouse

Learn more >

Christmas Gift Guide

Click for more ›

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Walid Mikhael

Brother QL-820NWB Professional Label Printer

It’s easy to set up, it’s compact and quiet when printing and to top if off, the print quality is excellent. This is hands down the best printer I’ve used for printing labels.

Ben Ramsden

Sharp PN-40TC1 Huddle Board

Brainstorming, innovation, problem solving, and negotiation have all become much more productive and valuable if people can easily collaborate in real time with minimal friction.

Sarah Ieroianni

Brother QL-820NWB Professional Label Printer

The print quality also does not disappoint, it’s clear, bold, doesn’t smudge and the text is perfectly sized.

Ratchada Dunn

Sharp PN-40TC1 Huddle Board

The Huddle Board’s built in program; Sharp Touch Viewing software allows us to easily manipulate and edit our documents (jpegs and PDFs) all at the same time on the dashboard.

George Khoury

Sharp PN-40TC1 Huddle Board

The biggest perks for me would be that it comes with easy to use and comprehensive programs that make the collaboration process a whole lot more intuitive and organic

David Coyle

Brother PocketJet PJ-773 A4 Portable Thermal Printer

I rate the printer as a 5 out of 5 stars as it has been able to fit seamlessly into my busy and mobile lifestyle.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?