A powerful new type of Internet attack works like a telephone tap, but it operates between computers and Web sites they trust.
at the Black Hat and DefCon security conferences have revealed a
serious flaw in the way Web browsers weed out untrustworthy sites and
block anybody from seeing them. If a criminal infiltrates a network, he
can set up a secret eavesdropping post and capture credit-card numbers,
passwords and other sensitive data flowing between computers on that
network and sites their browsers have deemed safe.
In an even more nefarious plot, an attacker could hijack the
auto-update feature on a victim's computer, and trick it into
automatically installing malware pulled in from a hacker's Web site.
The computer would think it's an update coming from the software
The attack was demonstrated by three hackers. Independent
security researcher Moxie Marlinspike presented alone, while Dan
Kaminsky, with Seattle-based security consultancy IOActive Inc., and
security and privacy researcher Len Sassaman presented together.
They reached essentially the same conclusion: There
are major problems in the way browsers interact with Secure Sockets
Layer (SSL) certificates, which is a common technology used on banking,
e-commerce and other sites handling sensitive data.
Browser makers and the companies that sell SSL certificates are working on a fix.
Microsoft Corp., whose Internet Explorer browser
is the world's most popular, said it was investigating the issue.
Mozilla Corp., which makes the No. 2 Firefox browser, said most of the
problems being addressed were fixed in the latest version of its
browser, and that the rest will be fixed in an update coming this week.
VeriSign Inc., one of the biggest SSL certificate companies, maintains that its certificates aren't vulnerable.
Tim Callan, a product-marketing executive in VeriSign's SSL
business unit, added that the "tap" won't work against so-called
Extended Validation SSL certificates, which cost more and involve a
deeper inspection of a company's application for a certificate.
The attack falls into a class of hacks known as
"man-in-the-middle," in which a criminal plants himself between a
victim's computer and a legitimate Web site and steals data as it moves
back and forth.
Jeff Moss, founder of the Black Hat and Defcon conferences who
this summer was appointed to the Homeland Security Department's
advisory council, said the fact a hacker has to actually break into a
victim's network for the attack to work can limit its usefulness.
"That's the nice mitigating thing," he said.
But he warned that "for targeted attacks it's absolutely deadly.
This is the way you can get everything. If you can get in the middle,
you can get everything. It's a big, giant wake-up call for the
SSL certificates are a critical technology in assigning trust on the Web.
Sites buy them to encrypt traffic and assure visitors it's OK to
enter confidential information. Companies that sell SSL certificates
verify that someone trying to buy a certificate actually owns the site
that certificate will be attached to.
The presence of an SSL certificate on a site is designated by a
padlock in the address bar. But many people don't pay attention to
whether a padlock is present or not.
Browsers do care, though, which is why last week's talks were significant.
Browsers are programmed to block sites that don't have a valid
SSL certificate, or have a certificate displaying a Web address that
doesn't match the address a Web surfer was trying to reach (which can
indicate someone has hijacked a person's Internet session). If the
sites aren't blocked, users are warned about potential danger and have
the option to click through.
The problems outlined by researchers center on a quirk in the way browsers read SSL certificates.
Many SSL certificate companies will allow people to attach a
programming symbol called a "null character" into the Web address onto
the certificates they receive. Web browsers generally ignore that
symbol. They stop reading at that symbol when they're checking the Web
address on a certificate.
The trick in the latest type of attack is that all a criminal
would need to do is put the name of a legitimate Web site before that
character, and the browser will believe that the site it's visiting -
which is under the criminal's control - is legitimate.
The criminal could then forward the traffic onto the legitimate
site and spy on everything the victim does on that site. It's a
complicated attack, but it highlights a significant weakness in the
very technology widely used to assure people it's safe to navigate
Jon Miller, an SSL expert and director of Accuvant Labs, said
he expects significant attacks against corporations using this
technique in the coming months. Criminals who run "phishing" scams, in
which people are tricked into visiting phony sites, will also likely
"What kind of makes this earth-shattering is these aren't the
most sophisticated attacks in the world," he said. "This is going to
become a huge problem."
There are signs it's already starting.
VeriSign's Callan said within hours of the talks, his company
got a number of applications for SSL certificates featuring null
characters, but they were denied.