Feeds

It's ba-ack. Exploit revives slain browser history bug

Attack reveals recently visited websites

Securing Web Applications Made Simple and Scalable

A Google researcher has resurrected an attack that allows website operators to steal the browsing history of visitors almost a year after all major browser makers introduced changes to close the gaping privacy hole.

Proof-of-concept code recently posted by Google security researcher Michal Zalewski works against the majority of people using the Internet Explorer, Chrome, and Firefox browsers. In an informal test carried out by The Register, the attack was able to list recently visited sites on computers running both Microsoft Windows and Apple OS X. It worked even though all three browser makers have patched their wares to stop them from divulging the addresses of sites visited over the past month or so.

“My proof of concept is fairly crude, and will fail for a minority of readers,” Zalewski wrote. “But in my testing, it offers reliable, high-performance, non-destructive cache inspection that blurs the boundary between :visited and all the 'less interesting' techniques.”

Previous exploits usually exploited a mechanism built into all browsers that causes recently visited websites to appear differently than non-visited sites. Attacks based on the CSS, or cascading style sheet, definitions weren't merely theoretical. Last year, academic researchers caught YouPorn.com and 45 other sites pilfering visitors' surfing habits by targeting the browser vulnerability, which first came to light more than a decade earlier

Zalewski said browser makers closed the hole by “severely crippling” CSS functions built around the :visited selectors. His proof-of-concept, according to comments accompanying the sourcecode (link may not work in all browsers), takes a different approach known as cache timing. It starts by loading an iframe tag containing a list of website into the page accessed by the visitor. It then calculates how quickly the websites are rendered. Those that load more quickly must be stored on the browser cache, an indication they have been visited recently.

Cache timing has long been identified as a way to extract browsing history, as noted in a well-known paper (PDF) penned by Princeton University computer scientist Ed Felten. Up to now, the problem with the approach has been that the attacks were slow and easy to detect, making them impractical.

Zalewski said his method was able to overcome these disadvantages by allowing browsers to abort the underlying request quickly. As a result, it's able to test about 50 websites per second with no visible signs that anything is amiss. With minor tweaks – including optimizations, parallelism, and possibly a delay calibration, the code could be capable of detecting “several hundred” URLs. ®

Mobile application security vulnerability report

More from The Register

next story
LibreSSL RNG bug fix: What's all the forking fuss about, ask devs
Blow to bit-spitter 'tis but a flesh wound, claim team
Manic malware Mayhem spreads through Linux, FreeBSD web servers
And how Google could cripple infection rate in a second
NUDE SNAPS AGENCY: NSA bods love 'showing off your saucy selfies'
Swapping other people's sexts is a fringe benefit, says Snowden
Own a Cisco modem or wireless gateway? It might be owned by someone else, too
Remote code exec in HTTP server hands kit to bad guys
British data cops: We need greater powers and more money
You want data butt kicking, we need bigger boots - ICO
Crooks fling banking Trojan at Japanese smut site fans
Wait - they're doing online banking with an unpatched Windows PC?
NIST told to grow a pair and kick NSA to the curb
Lrn2crypto, oversight panel tells US govt's algorithm bods
prev story

Whitepapers

Reducing security risks from open source software
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Consolidation: The Foundation for IT Business Transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.
Application security programs and practises
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Consolidation: the foundation for IT and business transformation
In this whitepaper learn how effective consolidation of IT and business resources can enable multiple, meaningful business benefits.