Three security research firms have noted a recent spike in TeslaCrypt ransomware over the last week. Experts believe the rise has been facilitated by the WordPress content management system (CMS).

The Ad Is the Poison

According to Ars Technica, the attack silently redirects visitors from original sites to malicious ones. The malicious sites host code from the Nuclear exploit kit (EK), while the WordPress sites are injected with large amounts of code that perform a silent redirection to domains displaying host ads. But this is only a diversion: Those ads are stuffed with more code that sends visitors to the true destination, the Nuclear EK.

If the visitors have out-of-date, unpatched versions of Adobe Flash Player, Adobe Reader, Microsoft Silverlight or Internet Explorer, they put themselves at risk for infection by the TeslaCrypt ransomware. This malware encrypts user files and then demands ransom for their decryption key.

Distinguishing Features

Security firm Sucuri noted that there were distinguishing features of the malware, including the fact that it had 32 hex-digit strings at the beginning and end of the code. Similarly, once the code has been decrypted it always looks the same.

Interestingly, the malware only infects first-time visitors to the infected site. Ars Technica noted that it may exhibit this sort of behavior in order to throw off security researchers, while Sucuri made sure to mention the invisible iframes installed as part of this process.

The URLs of the invisible iframe all use third-level domains and have “Admedia” or “advertizing” in the path. All the malicious domains and subdomains point to servers on Digital Ocean’s network: 46.101.84.214, 178.62.37.217, 178.62.37.131 and 178.62.90.65.

TeslaCrypt Ransomware Opens Backdoors

TeslaCrypt also uploads multiple backdoors into various locations on the affected Web server and frequently updates the injected code. That means it reinfects all the JavaScript files it can access using cross-site contamination as the method. A webmaster will have to sanitize all the sites on the server at the same time, not just the obviously affected ones, to truly clear out the infection.

Unless the TeslaCrypt problem is resolved, users — and site owners, in particular — should ensure that they are using unique passwords and have the latest versions of patched products.