25,000 Fortinet Devices Vulnerable To DUHK Attacks

Over 25,000 Fortinet devices used for vpn connections and accessible via the Internet are vulnerable to a new DUHK cryptographic attack, allowing attackers to decrypt passive vpn connections to read traffic.

DUHK stands for Do not Use Hard-coded Keys and was developed by Matthew Green , cryptographer and professor at Johns Hopkins University, in collaboration with Nadia Heninger and Shaanan Cohney. Vulnerability occurs with the ANSI X9.31 Random Number Generator (RNG) in combination with a hard-coded seed key. The ANSI X9.31 RNG is a more than 20 year old algorithm that was used to recently to generate cryptographic keys that are used to protect vpn connections and web sessions so that third parties can not intercept.

Through the DUHK attack, an attacker of vulnerable implementations can detect the secret encryption key, thus decrypting and reading traffic from vpn connections and web sessions. This may include sensitive information, such as company information, login information, credit card information, and other confidential content. The ANSI X9.31 RNG is used in many government-certified products. Until last year, ANSI X9.31 RNG was one of four number-generators approved by the United States for use in cryptographic modules. However, it has been removed from the list.

Network manufacturer Fortinet made use of this vulnerable number generator. It's about devices with FortiOS 4.x. All Fortinet vpn devices with FortiOS 4.3.0 to FortiOS 4.3.18 can be decrypted by a passive network attacker who can detect encrypted handshake traffic. Fortinet released FortiOS 4.3.19 last year to update the problem. According to Green, there are more than 25,000 vulnerable vpn devices on the Internet. The professor argues that it is a "conservative number", as only machines were counted that responded to the researchers' scans. The researchers have published a document with their findings ( pdf ) but will not disclose the attack code.

EFF Advises Against Eavesdropping HTTPS And VPN By NSA

This week, researchers presented information showing that the NSA may be able to store some encrypted connections, such as HTTPS, SSH and VPN, eavesdrop. Users can, however, take steps to prevent this, according to the American civil rights movement EFF.

The problem is that is used when an encrypted connection for instituting an algorithm for exchanging the key. In many cases, used for this purpose is the Diffie-Hellman algorithm. It forms the basis for modern cryptography and is used for VPNs, HTTPS, email, and other protocols. Because of the way the algorithm is implemented users run the risk of being bugged by the secret services, researchers said Alex Halderman and Nadia Heninger.

The problem is that a client, for example, a browser, and a server which use Diffie-Hellman must first agree on a prime number with a certain shape. Many applications thereby appear to use standardized 'hardcoded' primes. A secret service that any one particular prime number is able to "crack", then can eavesdrop all connections that use this particular prime number. It is in this case 1024-bit prime numbers.

NSA

"Based on the evidence we have, we can not prove that the NSA does. Our proposed way to crack Diffie-Hellman is better suited to the technical details of the large-scale decryption capabilities of the NSA than any other explanation," said the researchers. The documents from whistleblower Edward Snowden that the NSA have an infrastructure to monitor VPN connections. The system is designed to collect specific data that is required specifically to attack Diffie-Hellman.

"As the use of Diffie-Hellman in this feeble way is widespread in both standards and implementations, it may take years before the problems are resolved," as the researchers warn. They argue that all major governments can carry out similar attacks, if they do not do that.
Actions

Internet users who want to protect themselves against a possible attack may take various measures. Diffie-Hellman can be in the browser are so turned off, so that with it the setting up of an encrypted connection no use is made. Users of VPN have set their software to Diffie-Hellman is used only with 2048-bit prime., As the EFF in this article explains