Feeds

Researcher raids browser history for webmail login tokens

Point, click, and hijack

High performance access to file storage

In a disclosure that has implications for the security of e-commerce and Web 2.0 sites everywhere, a researcher has perfected a technique for stealing unique identifiers used to prevent unauthorized access to email accounts and other private resources.

Websites typically append a random sequence of characters to URLs after a user has entered a correct password. The token is designed to prevent CSRF (cross-site request forgery) attacks, which trick websites into executing unauthorized commands by exploiting the trust they have for a given user's browser. The token is generally unique for each user, preventing an attacker from using CSRF attacks to rifle through a victim's account simply by sending a generic URL to a website.

Now, a researcher who goes by the name Inferno has come up with a way to guess CRSF tokens using brute forcing techniques by combining it with a much older attack. As researchers have pointed out for years, it's trivial for website owners to steal a complete copy of most people's recent browsing history using what's known as CSS history hacking. By checking each visitor for a long list of possible tokens belonging to highly desirable websites (think Gmail, eBay, and the like), an unscrupulous webmaster can determine a CSRF token with minimal fuss.

It's "another neat little technique in the web hacker's toolbox, in the event that your target website doesn't have any XSS (cross-site scripting) issues," said Jeremiah Grossman, a web application security expert and the CTO of WhiteHat Security. "Once I have the token, then I can force you to make valid requests with your browser that'll work."

The technique has several advantages over current attacks. Namely, it runs entirely on the client, so web application firewalls and intrusion detection devices used by websites are generally blind to the attack. Inferno admits that the method is generally useful for guessing tokens that are relatively short. A base16 token with a length of five character generated about 393,216 requests, he noted.

"I tried it on a base16 string of length 5 and was able to brute force the entire key space in less than 2 minutes," he wrote here.

The new technique has some important implications for the way webmasters should issue tokens. For one thing, tokens should contain eight or more more characters - though with the breakneck growth of computer processing power, that number will be sure to rise.

Inferno recommended that websites employ other countermeasures, including storing CSRF tokens as part of a hidden form field rather than putting it in a URL and using a different random token for each form submission. ®

High performance access to file storage

More from The Register

next story
Obama allows NSA to exploit 0-days: report
If the spooks say they need it, they get it
OpenSSL Heartbleed: Bloody nose for open-source bleeding hearts
Bloke behind the cockup says not enough people are helping crucial crypto project
Web data BLEEDOUT: Users to feel the pain as Heartbleed bug revealed
Vendors and ISPs have work to do updating firmware - if it's possible to fix this
One year on: diplomatic fail as Chinese APT gangs get back to work
Mandiant says past 12 months shows Beijing won't call off its hackers
Call of Duty 'fragged using OpenSSL's Heartbleed exploit'
So it begins ... or maybe not, says one analyst
Heartbleed exploit, inoculation, both released
File under 'this is going to hurt you more than it hurts me'
Experian subsidiary faces MEGA-PROBE for 'selling consumer data to fraudster'
US attorneys general roll up sleeves, snap on gloves
Bad PUPPY: Undead Windows XP deposits fresh scamware on lawn
Installing random interwebs shiz will bork your zombie box
prev story

Whitepapers

Mainstay ROI - Does application security pay?
In this whitepaper learn how you and your enterprise might benefit from better software security.
Five 3D headsets to be won!
We were so impressed by the Durovis Dive headset we’ve asked the company to give some away to Reg readers.
3 Big data security analytics techniques
Applying these Big Data security analytics techniques can help you make your business safer by detecting attacks early, before significant damage is done.
The benefits of software based PBX
Why you should break free from your proprietary PBX and how to leverage your existing server hardware.
Mobile application security study
Download this report to see the alarming realities regarding the sheer number of applications vulnerable to attack, as well as the most common and easily addressable vulnerability errors.