Google, Microsoft and Yahoo fix serious email weakness
Use of weak DKIM signing keys could allow spoofed email messages to look legitimate, US-CERT warned
IDG News Service - Google, Microsoft and Yahoo have remedied a cryptographic weakness in their email systems that could allow an attacker to create a spoofed message that passes a mathematical security verification.
The weakness affects DKIM, or DomainKeys Identified Mail, a security system used by major email senders. DKIM wraps a cryptographic signature around an email that verifies the domain name through which the message was sent, which helps more easily filter out spoofed messages from legitimate ones.
The problem lies with signing keys that are less than 1,024 bits, which can be factored due to increasing computer power. US-CERT said in an advisory issued Wednesday that signing keys less than 1,024 bits are weak, and that keys up to RSA-768 bits have been factored.
The issue came to light after Florida-based mathematician Zachary Harris was sent an email from a Google recruiter that used only a 512-bit key, according to a report published Wednesday by Wired magazine.
Thinking it might be some clever test by Google, he factored the key, then used it to send a spoofed message from Sergey Brin to Larry Page, Google's founders.
It wasn't a test but in fact a serious problem, one in which emails that could be bogus would be trusted. According to the DKIM standard, email messages that have keys shorter that 1,024 bits are not necessarily rejected.
Harris found the problem wasn't limited to Google, but also Microsoft and Yahoo, all of whom appeared to have fixed the issue as of two days ago, according to US-CERT. Harris told Wired he found either 512-bit or 768-bit keys in use at PayPal, Yahoo, Amazon, eBay, Apple, Dell, LinkedIn, Twitter, SBCGlobal, US Bank, HP, Match.com and HSBC.
Weak signing keys are a boon for cybercriminals. They selectively target people with emails containing malicious links in an attempt to exploit a computer's software and install malware, a style of attack known as spear phishing. If an email contains the correct DKIM signature, it's more likely to end up in a recipient's inbox.
US-CERT also warned of another problem. The DKIM specification allows a sender to flag that it is testing DKIM in messages. Some recipients will "accept DKIM messages in testing mode when the messages should be treated as if they were not DKIM signed," US-CERT said.
Send news tips and comments to firstname.lastname@example.org. Follow me on Twitter: @jeremy_kirk
- 15 Non-Certified IT Skills Growing in Demand
- How 19 Tech Titans Target Healthcare
- Twitter Suffering From Growing Pains (and Facebook Comparisons)
- Agile Comes to Data Integration
- Slideshow: 7 security mistakes people make with their mobile device
- iOS vs. Android: Which is more secure?
- 11 sure signs you've been hacked
- Pay-as-you-Grow Data Protection: IBM Tivoli's Full-featured Data Protection Suite for Small to Medium Businesses IBM Tivoli Storage Manager Suite for Unified Recovery gives small and medium businesses the opportunity to start out with only the individual solutions...
- Streamline Data Protection with IBM Tivoli Storage Manager Operations Center IBM Tivoli Storage Manager (TSM) has been an industry-standard data protection solution for two decades. But, where most competitors focus exclusively on Backup...
- Simplify and Consolidate Data Protection for Better Business Results Learn about IBM® Tivoli® Storage Manager Operations Center, which provides advanced visualization, built-in analytics and integrated workflow automation features that leapfrog traditional backup...
- HP HAVEn: See the big picture in Big Data HP HAVEn is the industry's first comprehensive, scalable, open, and secure platform for Big Data. Enterprises are drowning in a sea of data...
- Meg Whitman presents Unlocking IT with Big Data During this Web Event you will hear Meg Whitman, President and CEO, HP discuss HAVEn - the #1 Big Data platform, as well...
- The New Way to Work Knowledge Vault This Knowledge Vault focuses on how, in today's increasingly virtual world, it's more important than ever to engage deeply with employees, suppliers, partners,... All Encryption White Papers | Webcasts