CryptoWall ransomware is back with new version after two months of silence

CryptoWall 3.0 uses both the Tor and I2P anonymity networks for increased stealthiness

Attackers have started distributing a new and improved version of the CryptoWall file-encrypting ransomware program over the past few days, security researchers warn.

The new version, dubbed CryptoWall 3.0, uses localization and passes traffic to a site where users can pay for their decryption keys through two anonymity networks -- Tor and I2P (the Invisible Internet Project).

CryptoWall is a sophisticated ransomware program that encrypts the victims' files with a strong cryptographic algorithm. Users are asked to pay the equivalent of US$500 in bitcoin virtual currency in order to receive the decryption key that allows them to recover their files.

The ransomware program provides users with links to several sites that act as Tor gateways. These proxy servers are supposed to automatically connect the user's browser to the CryptoWall decryptor service hosted on the Tor network. However, it seems that with CryptoWall 3.0, the user's traffic is also passed through another anonymity network called I2P.

A malware researcher who uses the online alias Kafeine discovered this change after infecting his test system with a CryptoWall 3.0 sample. When he tried to visit one of the Tor gateway links as instructed by the malware he received an error in Russian that roughly translates to: "I2P website is unavailable. Perhaps it is disabled, the network is congested or your router is not well integrated with other nodes. You can repeat the operation."

This suggests that the site where users can pay the ransom and get their decryption keys from is no longer hosted on Tor, but on I2P. The Tor gateway likely passes the user's traffic to a Tor hidden service first, which then connects to the I2P network to retrieve the real website. The ransom note also instructs users to download the Tor browser and access a Tor hidden service directly if the Tor gateway URLs no longer work.

CryptoWall is not the first malware program to use I2P. In November 2013, security researchers reported that an online banking Trojan called i2Ninja was being advertised on cybercriminal forums. The program communicated with a command-and-control server hosted on the I2P network, instead of Tor.

Like Tor, the I2P network allows users to run hidden services such as websites that are only accessible from within the network itself. With Tor such websites use the .onion pseudo-top-level domain, while with I2P they use .i2p.

A new version of Silk Road, an online marketplace for illegal goods and services, was recently launched on I2P. The site was previously hosted on Tor and was shut down two times by the FBI.

Cybercriminals started distributing CryptoWall 3.0 Monday, after around two months of inactivity that made researchers wonder whether the threat was gone.

Like its predecessors, the new version is being distributed through drive-by download attacks that exploit vulnerabilities in outdated browser plug-ins or through other malware already installed on computers, researchers from Microsoft said Tuesday in a blog post.

According to Kafeine, depending on the victim's location, the malware might also display the ransom note and instructions in a different language. For example, on his test system he received the CryptoWall instructions in French.

Users should back up their files regularly to a storage device that is then disconnected from the computer and network to prevent the backups from also getting encrypted by a CryptoWall infection. In the absence of backups there is usually no option to recover the files aside from paying cybercriminals for the decryption key.

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