A newly discovered derivative of CryptoMix ransomware, dubbed CryptoShield 1.0, is reportedly one of the latest malicious tools to be adopted by the ElTest malware campaign. And while it’s name may convey images of armored protection, it is very much used an an offensive weapon.
A ProofPoint security researcher who goes by the alias Kafeine recently uncovered the variant, which is delivered to victims via the RIG exploit kit, as first reported by BleepingComputer. RIG is a staple of the ElTest campaign, which compromises legitimate, vulnerable websites with malicious code so that visitors are redirected to a page that downloads the EK.
Once the main ransomware payload is downloaded and executed, CryptoShield generates an encryption key and unique ID for the infected machine and sends them to its command-and-control server before encrypting the victim’s files with AES-256 encryption. There is no effective decryption tool for this malware.
The delivery of the ransom note itself seems a bit inelegant.
CryptoShield displays a fake alert, written in poor English, that notifies the user of an application error in explorer.exe, aka Windows Program Manager. The alert prompts the victim to click the “Yes” button in the next window in order to restore explorer.exe. Clicking “OK” leads to this secondary window, which asks the user permission to execute a particular command that bypasses Windows User Access Control. Clicking “Yes” as instructed restarts the ransomware and displays the ransom note, copies of which are also saved to any folder that contains an encrypted file.
The note warns victims that they have 72 hours to pay before the ransom price doubles. It is not clear how much the cybercriminals are initially asking for. The note also contains the victim’s ID, and three email addresses for contacting the ransom developer for payment instructions.
SC Media contacted Proofpoint and Kafeine for additional context, and will update the story, pending a response.