Feeds

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

Attack reveals recently visited websites

Choosing a cloud hosting partner with confidence

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. ®

Beginner's guide to SSL certificates

More from The Register

next story
Russian hackers exploit 'Sandworm' bug 'to spy on NATO, EU PCs'
Fix imminent from Microsoft for Vista, Server 2008, other stuff
FYI: OS X Yosemite's Spotlight tells Apple EVERYTHING you're looking for
It's on by default – didn't you read the small print?
Microsoft pulls another dodgy patch
Redmond makes a hash of hashing add-on
'LulzSec leader Aush0k' found to be naughty boy not worthy of jail
15 months home detention leaves egg on feds' faces as they grab for more power
Forget passwords, let's use SELFIES, says Obama's cyber tsar
Michael Daniel wants to kill passwords dead
Kill off SSL 3.0 NOW: HTTPS savaged by vicious POODLE
Pull it out ASAP, it is SWISS CHEESE
Facebook slurps 'paste sites' for STOLEN passwords, sprinkles on hash and salt
Zuck's ad empire DOESN'T see details in plain text. Phew!
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Cloud and hybrid-cloud data protection for VMware
Learn how quick and easy it is to configure backups and perform restores for VMware environments.
Three 1TB solid state scorchers up for grabs
Big SSDs can be expensive but think big and think free because you could be the lucky winner of one of three 1TB Samsung SSD 840 EVO drives that we’re giving away worth over £300 apiece.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.