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CryptoMix Ransomware Variant EXTE Emerges

A new variant of the CryptoMix ransomware was recently observed, appending the .EXTE extension to targeted files, security researchers warn.

A new variant of the CryptoMix ransomware was recently observed, appending the .EXTE extension to targeted files, security researchers warn.

Around for over a year, the CryptoMix ransomware family has seen numerous updates over time, but few major changes appear to have been added to it: although the ransom note and the used extension suffered modifications, the encryption method remained nearly the same from one variant to the other.

Once executed on the victim’s computer, the ransomware drops a file in the ApplicationData folder, while also dropping the ransom note in the targeted files’ folders. The malware also adds a series of registry keys, creates a unique ID and sends it to a remote location, after which it starts encrypting files using AES encryption.

In the ransom note, the malware demands users to contact the author via provided email addresses, while also asking them to pay the ransom amount in Bitcoins.

Discovered by Malwarebytes’ Marcelo Rivero, the latest malware variant uses the same encryption method as previous iterations, but does show some small updates, BleepingComputer’s Lawrence Abrams reveals.

The threat now adds the .EXTE extension to the encrypted files’ encrypted file name, while using a new ransom note named _HELP_INSTRUCTION.TXT (last year, CryptoMix used the HELP_YOUR_FILES.TXT ransom note). In this campaign, users are required to contact the ransomware authors at [email protected], [email protected], and [email protected] for payment information.

Earlier this month, a different variant of the malware was observed appending the .AZER extension to the encrypted files and using the _INTERESTING_INFORMACION_FOR_DECRYPT.TXT ransom note and [email protected] and [email protected] email addresses.

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Unlike previous variants, the AZER CryptoMix iteration performs no network communication and is completely offline. It embeds ten different RSA-1024 public encryption keys and uses one of them to encrypt the AES key it uses to encrypt the files. 

The EXTE version, Abrams points out, also embeds the ten public RSA keys, meaning it too can work offline. The two variants emerged about one week of each other, which shows that the actor behind this ransomware variant is highly active. Since the beginning of this year, at least three other CryptoMix variants emerged: Wallet, CryptoShield, and Mole02.

Related: RIG Exploit Kit Drops New CryptoMix Ransomware Variant

Related: Ransomware Operators Show Reputable “Customer” Service

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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