RSAUtil Ransomware Distributed via RDP Attacks

11.5.2017 securityweek Ransomware
The author of a newly discovered ransomware family is hacking into remote desktop services to upload the malware alongside a bunch of other tools.

Dubbed RSAUtil, the ransomware is written in Delphi and appends the extension to the encrypted files, Emsisoft malware researcher xXToffeeXx revealed on Twitter. The malware also drops a How_return_files.txt ransom note in every folder.

In addition to the malware itself, the package of files that the malware’s developer drops after hacking into remote desktop services includes a variety of tools and a config file meant to determine how the ransomware executes, BleepingComputer’s Lawrence Abrams notes.

The package is meant to prepare the machine for the installation of RSAUtil ransomware. A CMD file cleans up traces of how the machine was compromised by clearing event logs; two files prevent the computer from going to sleep or hibernating, so that the connection remains active; an image file is supposedly used as desktop background; and a bat file is used to configure various remote desktop services options.

There is also a configuration file the ransomware uses when performing the encryption process, containing directives that check whether the computer has been encrypted already, what ID the malware should use, what email to use, the ransom note name, the encrypted file extension, and the public encryption key to use to encrypt files.

RSAUtil ransomware is included in the package under the name of svchosts.exe. It scans the computer’s folders, along with mapped network drives and unmapped network shares, and encrypts user’s files. It also places a ransom note in every folder where a file has been encrypted.

The malware doesn’t target a specific list of file types to encrypt, which means that many of the executables on the machine end up being encrypted as well. The specific sample researchers analyzed in this case was appending the extension to the encrypted files.

When completing the encryption process, the malware displays a lock screen informing the victim to contact the malware author at or to receive information on how to pay the ransom. Once the payment is made, the victim receives a decryption key to input in the lock screen and regain access to the files.

Files encrypted by RSAUtil can’t be restored for free at the moment. Regardless, users are advised to refrain from paying the ransom, as that doesn’t guarantee they would actually be able to restore their files. Keeping all data backed up can prove very helpful in the event of ransomware compromise.