The SANS Internet Storm Center reports that the Blank Slate spam campaign which was first detected in July last year is now being used to spread Cerber ransomware, rather than previous favorites Locky and Sage 2.0.
In the majority of cases, emails used to spread ransomware and other nasties use a variety of social engineering techniques to trick end users into opening the email attachments and infecting their computers. However, the Blank Slate spam campaign opts for simplicity. The spam email messages contain no text, hence the name ‘blank slate’.
The email messages contain a double zip file attachment. A zip file is attached to the email, and within it is a second zip file containing JavaScript or a Word document with a malicious macro. The JavaScript or macro then downloads the malicious payload – Cerber ransomware – if it is run.
Without any social engineering tactics, infection rates are likely to be much lower. However, researchers suggest that more email messages are likely to get past security defenses using this technique. Since more emails are delivered to end users’ inboxes, this is likely to make up for the fact that fewer attachments will be opened. The blank slate spam campaign is believed to be spread via botnets.
Cerber ransomware has been a major threat over the past 12 months. The ransomware is frequently updated to ensure it avoids detection. The latest blank slate spam campaign is being used to spread the latest form of the ransomware, which hides malicious code inside Nullsoft Scriptable Install System (NSIS) installers.
Security researchers at Palo Alto Network’s Unit 42 team report that Cerber ransomware is being hosted on around 500 separate domains. When domains are detected by hosting companies they are rapidly shut down; however, new domains are then registered by the criminals to take their place.
Since new domains can easily be registered using stolen credentials, the costs to cybercriminals are low. The cost of signing up for a new domain are negligible. Burner phones can be purchased cheaply and the numbers provided when registering domains, email addresses can be registered free of charge, and stolen credit card details can be used to make payment. There is no shortage of stolen credit card numbers to use. However, the rewards from Cerber ransomware infections are high. Now, the keys to decrypt data locked by Cerber ransomware costs victims 1 Bitcoin – around $1,000.
Organizations can protect against the threat by ensuring their spam filtering solutions are carefully configured and making sure all employees are instructed never to open JavaScript files or enable Word macros sent from unknown senders.