Feeds

Hole in Yahoo! surrenders keys to the kingdom

Attack of the killer XSS

Seven Steps to Software Security

Yahoo has closed a gaping hole that attackers were exploiting to gain access to victims' Yahoo Mail accounts and other restricted areas of site.

The cross site scripting error in the hotjobs.yahoo.com domain allowed the attackers to inject cleverly obfuscated javascript into the page that silently siphoned the cookies used to authenticate Yahoo users when they log in to sections of the portal that require a password. Armed with the cookies, attackers were then given broad control over the victim's Yahoo account, including Yahoo Email and any other service that uses authentication cookies belonging to the yahoo.com domain.

"I guess the beautiful bit about it from an attacker's viewpoint is quite a lot of people would be unaware of what's happened" after accessing a booby-trapped hotjobs URL, said Paul Mutton, an internet services developer for Netcraft who helped discover the exploit. "Not many people will think of changing their password after that happens."

To Yahoo's credit, Mutton said the XSS error was closed within hours of him reporting it to Yahoo's security team. But the episode is a reminder that even the biggest sites can be needlessly sloppy when it comes to handling authentication cookies. The attack would have been impossible to carry out had Yahoo bothered to use http-only cookies.

Yahoo is hardly alone here. Last month, bankofamerica.com, register.com, netflix.com and dozens of other big name sites were caught transmitting credentials that are vulnerable to a new tool called CookieMonster. That attack is neutered when sites use https-only cookies.

A Yahoo spokeswoman thanked Netcraft for help identifying the problem. She reminded users of the importance of resetting passwords. That's a sensible precaution, but it would have done nothing to protect users against this attack.

According to Mutton, XSS vulnerability was exploited by hotjobs.com URLs that contained a long series of digits. When transformed into javascript it redirected users to a blank webpage on a different domain. A victim need not enter a user name or password. Visiting the blank page was all that was required to steal an authentication cookie that acts as a universal key across the the entire yahoo.com domain.

At time of writing, the blank page remained up and running. It's unknown if it's being used to attack other websites. Netcraft's report is here. ®

Mobile application security vulnerability report

More from The Register

next story
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
Mozilla fixes CRITICAL security holes in Firefox, urges v31 upgrade
Misc memory hazards 'could be exploited' - and guess what, one's a Javascript vuln
BMW's ConnectedDrive falls over, bosses blame upgrade snafu
Traffic flows up 20% as motorway middle lanes miraculously unclog
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
Yorkshire cops fail to grasp principle behind BT Fon Wi-Fi network
'Prevent people that are passing by to hook up to your network', pleads plod
Don't look, Snowden: Security biz chases Tails with zero-day flaws alert
Exodus vows not to sell secrets of whistleblower's favorite OS
Researcher sat on critical IE bugs for THREE YEARS
VUPEN waited for Pwn2Own cash while IE's sandbox leaked
prev story

Whitepapers

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.
How modern custom applications can spur business growth
Learn how to create, deploy and manage custom applications without consuming or expanding the need for scarce, expensive IT resources.
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.
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.