Rakhni ransomware, a malware variant first detected in 2013, has spawned many variants over the past three years and is still an active threat. Rakhni ransomware locks files on an infected device to prevent the user from accessing their data. A ransom demand is issued and if payment is made, the attackers will supply the keys to unlock the encryption. If the ransom is not paid the files will remain encrypted. In such cases, the only option for file recovery is to restore files from backups.
Now the developers of Rakhni ransomware have incorporated new functionality. Checks are performed on an infected device to determine whether it has sufficient processing power to be used as a cryptocurrency mining slave. If so, cryptocurrency mining malware will be downloaded. If not, ransomware will be deployed.
This new development should not come as a major surprise. The massive rise in the value of many cryptocurrencies has made mining cryptocurrencies far more profitable for cybercriminals than ransomware. When ransomware is installed, many victims choose not to pay and instead recover files from backups. Infection is no guarantee that a payment will be received. If a cryptocurrency miner can be installed, it gets straight to work generating money for the attackers. Ransomware attacks are still a major threat, although many cybercriminals have switched their operations to mining cryptocurrencies. In fact, cryptocurrency mining malware attacks are now much more common than ransomware attacks.
However, not all computers have sufficient CPU processing power to make cryptocurrency mining worthwhile, so the method used by the threat actors behind Rakhni ransomware helps them maximize their profits.
The new Rakhni ransomware campaign was detected by researchers at Kaspersky Lab. The malware used is Delphi-based and is being distributed in phishing emails containing a Microsoft Word file attachment.
The user is advised to save the document and enable editing. The document contains a PDF file icon which, if clicked, launches a fake error message suggesting the DLL file required to open the PDF file has not been found. The user needs to click on the OK box to close the error message.
When the error box is closed, the malware performs a series of checks on the machine to identify the processes running on the device and assesses those processes to determine if it is running in a sandbox environment and the likelihood of it being able to run undetected. After these checks have been performed the system is assessed to determine its capabilities.
If the machine has more than two processors and does not have a Bitcoin folder in the AppData folder, a cryptocurrency miner will be installed. The cryptocurrency miner uses fake root certificates which show the program has been issued by Microsoft Corporation to help disguise the miner as a trusted application.
If a Bitcoin folder does exist, certain processes will be stopped, and Rakhni ransomware will be downloaded and run. If there is no Bitcoin folder and only one processor, the malware will use its worm component and twill attempt to spread to other devices on the network where the process starts over.
Advanced anti-virus software can provide protection against this attack, while spam filtering solutions can prevent the phishing emails from being delivered to end users. Businesses should also ensure that their employees are made aware of the risk of these types of attacks through security awareness training. Employees should be instructed never to open attachments in emails from unknown senders and taught the warning signs of a potential attack in progress. Naturally, good data backup practices are essential to ensure that if all other controls fail, files can be recovered without paying a ransom.