The attackers first use the Pony computer Trojan to pilfer passwords from compromised computers, including FTP and SSH credentials that webmasters use to administer websites, according to researchers from Heimdal Security.
The stolen credentials are then used to inject malicious code into legitimate websites with the goal of redirecting their visitors to an installation of the Angler exploit kit. This is a Web-based attack tool that includes exploits for various vulnerabilities in Windows and browser plug-ins, such as Flash Player and Java.
Computers whose software is not up to date are specifically exposed to Angler attacks, which are known as drive-by downloads. If any of the exploits is successful, CryptoWall 4 is deployed on the computer.
CryptoWall is one of the most widespread and successful ransomware programs to date, having earned its creators millions of dollars in ransom payments. The application encrypts files using a strong cryptographic algorithm and then asks victims to pay for the encryption key.
In the absence of offline backups, many victims, including companies and government organizations, have been forced to pay in order to recover critical documents and other irreplaceable data.
This attack campaign is extensive and originates from a bulletproof hosting environment located in Ukraine, the Heimdal security researchers said in a blog post. "Because of the mechanisms involved and the attackers’ objectives, the campaign is prone to achieve large distribution and affect a big number of PCs and their users."