Researchers have sinkholed the command and control (C&C) domains used by the CryptoPHP malware and determined that tens of thousands of websites have been affected.
Netherlands-based security company Fox-IT published a paper on CryptoPHP on November 20. The threat is utilized to hijack websites powered by Joomla, WordPress and Drupal and abuse them for black hat search engine optimization (SEO).
The attackers distribute the backdoor by planting it inside themes and plugins for the popular content management systems (CMS). Once it’s deployed on a server, the malware can be controlled manually, or via email and C&C communications.
Fox-IT has been monitoring the evolution of the campaign with the help of Spamhaus, Abuse.ch, Shadowserver and the Dutch National Cybercrime Security Center (NCSC).
By sinkholing the C&C servers, researchers have managed to determine how many unique IP addresses connected to them. The total number reported last week was 23.693 unique IP addresses, but experts said they had been seeing a decline in sinkhole connections.
On November 22, a total of 20,305 IPs connected to the sinkhole, but by November 24 the number dropped to 16,786. The highest number of infections has been spotted in the United States (8,657), Germany (2,877), France (1,231), the Netherlands (1,008), and Turkey (749).
“These numbers are however not a clear indication, mostly because the servers connecting to our sinkholes were shared hosting with at least 1 or multiple backdoored websites. This means the actual affected websites will be higher,” Fox-IT’s Yonathan Klijnsma explained in a blog post.
Klijnsma told SecurityWeek that the NCSC is currently working on physically taking down the servers used in the CryptoPHP campaign. However, the expert has pointed out that such operations generally take a very long time.
Researchers haven’t been able to determine which CMS powers each of the affected websites since the attackers are using public key encryption for communications between the compromised server and the C&C. According to Fox-IT, the websites used to distribute CryptoPHP went offline on November 23, but they were brought back online the next day.
Multiple new versions of the threat have been discovered over the past week and their associated hashes have been added to a GitHub repository containing CryptoPHP indicators of compromise (IoC). The security firm has updated the Python tool it has developed to help administrators detect the threat.
Fox-IT has also published instructions on how to remove the threat from infected websites, but the company advises administrators to reinstall their CMS since the system’s integrity might have been compromised.