Yahoo leaks private key, allows anyone to build Yahoo-signed Chrome extensions

Yahoo accidentally leaked the private key that was used to digitally sign its new Axis extension for Google Chrome

Yahoo was forced to release a new version of its Axis extension for Google Chrome after the original one contained a private key that allowed anyone to digitally sign extensions in Yahoo's name.

Axis is a new search and browsing tool from Yahoo that was released on Wednesday. It is available for desktop computers, as an extension for Google Chrome, Mozilla Firefox, Internet Explorer and Safari, as well as for iOS devices, as a stand-alone app.

However, while looking at the source code for the Google Chrome Axis extension, hacker and security blogger Nik Cubrilovic discovered a serious security flaw -- the package included the private cryptographic key used by Yahoo to sign the extension.

"With access to the private certificate file [private key] a malicious attacker is able to create a forged extension that Chrome will authenticate as being from Yahoo," Nik Cubrilovic said in a blog post on Thursday.

Google Chrome extensions come packed as CRX files, which are essentially digitally signed ZIP-format archives.

Every CRX file contains a public key that's part of a private-public key pair unique to its creator. The private key is used to sign the extension, while the public key is used by the browser to verify the signature's authenticity.

Since private keys allow developers to digitally sign new extensions or update their old ones, they should always be kept secret.

In order to prove the implications of the private key leak, Cubrilovic created a proof-of-concept Chrome extension that displays an alert on every visited website and signed it with Yahoo's private key.

An attacker can push a Yahoo-signed malicious extension to a browser that has the Axis extension installed, by using techniques like DNS spoofing, Cubrilovic said.

Google Chrome automatically checks for extension updates by querying update URLs specified by developers. If attackers can forge the DNS (domain name system) responses received by the browser, they can force it to install a rogue digitally signed extension update from a server under their control.

Yahoo confirmed the security issue. "We worked quickly to resolve the issue and have issued a new Chrome plug-in," a Yahoo spokeswoman said via email. "Users who downloaded Yahoo! Axis on Chrome between the hours of 6-9 p.m. Pacific Time on May 23, 2012, are encouraged to uninstall the previous version and reinstall the new version at axis.yahoo.com."

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.
Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.
Lucian Constantin

Lucian Constantin

IDG News Service
Show Comments

Brand Post

Win pair of MOMENTUM True Wireless

Three PC World readers will be in the running to take home a pair of MOMENTUM True Wireless which are meticulously crafted with every fine listening detail considered. *T&C's Apply

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Jack Jeffries

MSI GS75

As the Maserati or BMW of laptops, it would fit perfectly in the hands of a professional needing firepower under the hood, sophistication and class on the surface, and gaming prowess (sports mode if you will) in between.

Taylor Carr

MSI PS63

The MSI PS63 is an amazing laptop and I would definitely consider buying one in the future.

Christopher Low

Brother RJ-4230B

This small mobile printer is exactly what I need for invoicing and other jobs such as sending fellow tradesman details or step-by-step instructions that I can easily print off from my phone or the Web.

Aysha Strobbe

Microsoft Office 365/HP Spectre x360

Microsoft Office continues to make a student’s life that little bit easier by offering reliable, easy to use, time-saving functionality, while continuing to develop new features that further enhance what is already a formidable collection of applications

Michael Hargreaves

Microsoft Office 365/Dell XPS 15 2-in-1

I’d recommend a Dell XPS 15 2-in-1 and the new Windows 10 to anyone who needs to get serious work done (before you kick back on your couch with your favourite Netflix show.)

Maryellen Rose George

Brother PT-P750W

It’s useful for office tasks as well as pragmatic labelling of equipment and storage – just don’t get too excited and label everything in sight!

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?