A team of researchers found out that several thousands of HTTPS-protected sites, mail servers and other popular Internet services are susceptible to a newly discovered encryption flaw that can put Web surfers' data at risk.

The bug, which is a bit similar to the FREAK attack, allows the attacker to weaken the encrypted connection shared by the user and the Web or email server. Otherwise known as Logjam, it affects all major browsers and any server that supports 512-bit Diffie-Hellman cryptography.

The flaw utilizes a man-in-the-middle attack, which downgrades the security of connections into a type of encryption that is in a much lower level (512 bit), making it easier to read and become vulnerable. Hence, organizations that have access to huge amounts of computing power such as the NSA could also break a much stronger encryption that employs the said algorithm.

"Millions of HTTPS, SSH, and VPN servers all use the same prime numbers for Diffie-Hellman key exchange," research on the vulnerability said. "Practitioners believed this was safe as long as new key exchange messages were generated for every connection. However, the first step in the number field sieve—the most efficient algorithm for breaking a Diffie-Hellman connection—is dependent only on this prime. After this first step, an attacker can quickly break individual connections."

The Logjam flaw moves particularly within a defined set of Diffie-Hellman algorithms that are responsible for the exchange of encryption keys prior to securing a connection. On the occasion that a Web browser talks to a server, an algorithm is expected to be agreed upon, which shall be used for the encrypted connection. Most of the time, the strongest type of algorithm is chosen. However, there are times when the Web server is tricked into opting for the weak one.

"It's actually a flaw in the SSL protocol that has been around for almost two decades," said Matthew D. Green, an assistant research professor at Johns Hopkins University's Department of Computer Science. He added that in order for the attacker to successfully trick the Web server into opting for a weaker key, the attacker should be on the same network that the targeted victim is in. For example, if the victim is in a coffee shop and using the place's Wi-Fi network, the attacker should also use the same Wi-Fi network.

Green, along with colleagues from Inria and the University of Michigan, discovered the vulnerability.

What the researchers are worried about are the email servers because a number of them were not upgraded after the FREAK attack.

"The big problem is that software people use to run email servers is not as well maintained," said Green. "They don't think about them. They just set them up and forget them. A lot of the default configurations that are shipped with them are bad ones."

Photo: Frankie Leon I Flickr

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