macOS users who had their systems infected with the FindZip ransomware can now use a decryption tool to restore their files without paying the ransom.
The ransomware was spotted last month by ESET, which detects it as OSX/Filecoder.E. An update to Apple’s XProtect signatures, however, started calling it FindZip soon after. Spreading through piracy sites, the threat masquerades as cracks for Adobe Premier Pro and Microsoft Office, and also feature signed certificates, though not by Apple.
FindZip is only the second piece of ransomware to target Mac users, but that doesn’t make it less destructive. In fact, the security researchers who analyzed the malware said at the time that victims had no way of recovering their files, because the malware was destroying the encryption key before attempting to communicate with the command and control server to send it to the attacker.
Because of that, the researchers recommended that users should not pay the ransom, as the attackers were believed to have no means of restoring encrypted files. However, while the recommendation remains, it appears that victims can recover their data, and can do so for free.
At the end of February, Malwarebytes Labs researchers published a post about how victims could restore their data using Xcode or TextWrangler, Xcode command-line tools, pkcrack source code, and both the encrypted and unencrypted versions of a file. A second computer or a different account on the compromised machine was also required, along with some technical knowledge.
Courtesy of Avast’s FindZip decryption tool, however, things are a bit simpler, and users can decrypt their files on either a Mac or a Windows machine. In fact, those victims who port their files from a Mac to Windows won’t need additional resources to install and use the decryptor, the researchers say.
On Mac or Linux, however, an emulation layer for Windows applications is required, and the tool has been already tested with CrossOver and Wine, though Avast says that other emulation programs might work as well. The decryption tool was tested on macOS 10.10 (Yosemite) and macOS 10.12 (Sierra).
Victims first need to install a windowing system for Mac, such as XQuartz, which is required to run Wine for Mac. If Wine was installed prior to the infection, chances are that all files are encrypted, and users are advised to delete the folder \Users\<YourUserName>\.wine before running the decryptor application.
When running the decryption tool, users might be prompted to install Mono, or Gecko, and Avast notes that they should hit Cancel if Mono is requested. After getting the application running, users will be required to select a location for the decrypted files, as well as a pair of original/encrypted files. At this point, they only need to wait for the tool to find the decryption password, and then start the recovery process. Users are advised to also opt-in to having the encrypted files backed up first.