Some victims of the recent Bad Rabbit attack may be able to recover their files encrypted by the ransomware without paying the ransom.

The discovery was made by researchers at Kaspersky Lab that analyzed the encryption functionality implemented by the ransomware.

Once the ransomware infects a computer, it encrypts certain file types, it also encrypts the disk and a ransom note is displayed when the computer boots.

The Bad Rabbit leverages the open source library DiskCryptor in order to encrypt the user files.

According to the preliminary analysis published by experts at the CSE Cybsec Zlab, the malware authors likely reused some pieces of NotPetya code increasing the complexity of the code itself and fixing coding errors that transform NotPetya from a ransomware to a wiper.

Now researchers from Kaspersky Lab discovered that files encrypted by Bad Rabbit can be recovered with following specific procedures.

When infected computer boots up, the victims are informed that their files have been encrypted by Bad Rabbit, and the malicious code provides instruction to complete the payment to obtain the decryption key.

Kaspersky noticed that Bad Rabbit uses the same screen to allows victims who have received the decryption key to enter it and boot their system.

Malware researchers discovered that after the ransomware the decryption key, this isn’t wiped from memory. Unfortunately, there is only a “slim chance” that victims will be able to extract the password.

The experts also discovered that Bad Rabbit does not delete shadow copies, allowing victims to restore the files through this windows backup functionality.

“We have discovered that Bad Rabbit does not delete shadow copies after encrypting the victim’s files. It means that if the shadow copies had been enabled prior to infection and if the full disk encryption did not occur for some reason, then the victim can restore the original versions of the encrypted files by the means of the standard Windows mechanism or 3rd-party utilities.” reads the analysis published by Kaspersky.

According to malware researchers, NotPetya has been linked to BlackEnergy APT, for this reason, some experts suggest the same threat actor could be behind the Bad Rabbit ransomware.

Pierluigi Paganini

(Security Affairs – Bad Rabbit ransomware, hacking)