Feeds

Windows 7 UAC flaw silently elevates malware access

Weak links in chain of trust

Securing Web Applications Made Simple and Scalable

Researchers have uncovered yet another flaw in Microsoft's Windows 7 beta that could allow attackers to gain full administrative privileges by bypassing the operating system's UAC, or user access control.

Researcher Rafael Rivera Jr. has released proof-of-concept code that demonstrates how unauthorized third-party software can elevate its privileges and install a potentially malicious payload on the latest version of Windows, which is still in beta. Researchers warn that anyone using the OS is vulnerable.

"Unfortunately this flaw is not just a single point of failure," writes security blogger Long Zheng. "The breadth of Windows executables is just too many and too diverse and many are exploitable."

The vulnerability stems from Microsoft's attempts to make UAC more palatable by allowing certain applications to make changes to the OS without first prompting the user for permission. Executables that are digitally signed are essentially given fast-track permission under UAC's default configuration. And it turns out many of these third-party executables are in turn able to invoke still more third-party code.

This gives rise to what Zheng calls "piggybacking," in which a proxy executable launches an elevated instance of rundll32.exe, a file that has existed in one form or another since before the days of Windows 95. Rundll32.exe can then point to a malicious payload, and because the payload has inherited the administrative privileges from its authorized parent process, UAC never prompts the user.

Rivera's proof-of-concept uses a one-line file called Catapult.exe as the proxy application that launches the rundll file. That in turn is able to execute a multi-line C++ program called Cake.dll, which reads the current process token and shows an on-screen message box. Of course, an attacker could do much more nefarious things.

A Microsoft spokesman said: "We are not aware of anyone impacted by this issue at this time, but it has already been addressed in a later internal beta build." In the meantime, Windows 7 users may want to set UAC to "high." ®

The smart choice: opportunity from uncertainty

More from The Register

next story
BMW's ConnectedDrive falls over, bosses blame upgrade snafu
Traffic flows up 20% as motorway middle lanes miraculously unclog
Putin: Crack Tor for me and I'll make you a MILLIONAIRE
Russian Interior Ministry offers big pile o' roubles for busting pro-privacy browser
Mozilla fixes CRITICAL security holes in Firefox, urges v31 upgrade
Misc memory hazards 'could be exploited' - and guess what, one's a Javascript vuln
Manic malware Mayhem spreads through Linux, FreeBSD web servers
And how Google could cripple infection rate in a second
How long is too long to wait for a security fix?
Synology finally patches OpenSSL bugs in Trevor's NAS
Don't look, Snowden: Security biz chases Tails with zero-day flaws alert
Exodus vows not to sell secrets of whistleblower's favorite OS
Roll out the welcome mat to hackers and crackers
Security chap pens guide to bug bounty programs that won't fail like Yahoo!'s
prev story

Whitepapers

Top three mobile application threats
Prevent sensitive data leakage over insecure channels or stolen mobile devices.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.