SSL is under attack once again, as this time two researchers claim to have come up with an attack tool, dubbed BEAST, that can crack SSL traffic used to secure Websites
Security researchers are set to unveil the attack tool
capable of breaking the encryption algorithm that protects Websites. Hours
before the presentation, cryptography experts provided recommendations on how
to defend Websites from the exploit.
Researchers Thai Duong and Juliano Rizzo are scheduled to
demonstrate BEAST, the Browser Exploit Against SSL/TLS attack tool, at the
Ekoparty security conference in Buenos Aires on Sept. 23. The tools target a long-documented
vulnerability in some encryption algorithms that researchers have long believed
were impractical to exploit.
"It is worth noting that the vulnerability that BEAST
exploits has been [present] since the very first version of SSL. Most people in
the crypto and security community have concluded that it is non-exploitable,
that's why it has been largely ignored for many years," Duong told
Secure Sockets Layer (SSL) is a standard protocol used by
millions of Websites to protect data as it moves between the user's computer
and the server the Website is hosted on. Originally invented in the 1990s, it
has been upgraded many times and is often referred to by the newer name
Transport Layer Security (TLS).
Duong and Rizzo said they've refined the attack to decrypt
the encrypted stream. The injection can be done through a malicious
advertisement, an iFRAME or other scripted elements. In a variation of a
"man in the middle" attack, the browser is tricked into executing the
code on the server.
Duong and Rizzo claimed the BEAST tool allows them to
intercept TLS "cookies," which are bits of text that identify users.
TLS cookies are frequently used by Websites to keep users logged in even after
the user has browsed off the page. They are expected to demonstrate the attack
during the Ekoparty presentation by recovering an encrypted cookie used to
access a user account on eBay's PayPal online payment service.
While exact details about the exploit tool are still
unknown, what is clear is that BEAST attacks algorithms that use a mode known
as cipher block chaining (CBC), in which information from a previously
encrypted block of data is used to encode the next block. AES and DES, two
strong cryptographic algorithms used to secure network and Web traffic, both
use CBC. The RC4 cipher does not.
Two-factor authentication service PhoneFactor recommended
Website owners reorganize "the way the data is sent in the encrypted
stream" and switch their sites to use the RC4 cipher to encrypt SSL
traffic. Google Web servers are apparently configured to favor RC4 over AES and
DES, according to the SSL Server Tool from Qualys. Many other Websites,
including PayPal, favors AES, making it vulnerable to BEAST-based attacks.
"Servers can protect themselves by requiring a non-CBC
cipher suite. One such cipher suite is rc4-sha, which is widely supported by
clients and servers," PhoneFactor's
Steve Dispensa wrote on the company blog.
Duong and Rizzo said BEAST targets TLS 1.0 and SSL 3.0, but
not the newer TLS 1.1 or 1.2 standards. However, very few Web sites are
actually using the newer and more secure versions, according to Ivan
Ristic from Qualys. While Website administrators can consider upgrading to
use TLS 1.1 or 1.2, but most Web browsers don't support the new standards. In
fact, Microsoft Internet Explorer 9 and Opera are the only Web browsers
currently supporting TLS 1.1 and TLS 1.2. Apple's Safari, Google Chrome and
Mozilla Firefox are still on TLS 1.0.
Google actually patched the developer version of Chrome to
thwart BEAST-based attacks without requiring sites to upgrade to TLS 1.1 or
1.2. The updated Chrome would split a message into fragments to reduce the
attacker's control over the plain text about to be encrypted, making it harder
for BEAST to decrypt the encrypted stream.
Kevin Liston, of the Internet Storm Center at the SANS
Institute recommended that users avoid using unknown Wireless networks to
access financial Websites and browser developers and server administrators
should move quickly to support TLS 1.2.
Duong and Rizzo have been working with browser makers since
May to develop a fix. "It's not the case that anything is 'broken,'"
Adam Langley, a security researcher for Google, posted on the Hacker News
Website. Langley said he was familiar with the details of the attack and said
"fundamentally there's nothing people should worry about."
PhoneFactor said upgrading the entire Web to use TLS 1.1 or
1.2 would be a "massive" undertaking.