Security researchers from Palo Alto Networks claims to have discovered the first OSX Ransomware, called KeRanger.
The ransomware comes bundled into the popular Mac app Transmission, a BitTorrent client with a lot of users.
From Palo Alto Networks:
The two KeRanger infected Transmission installers were signed with a legitimate certificate issued by Apple.
The KeRanger infected Transmission installers include an extra file named General.rtf in the Transmission.app/Contents/Resources directory. It uses an icon that looks like a normal RTF file but is actually a Mach-O format executable file packed with UPX 3.91. When users click these infected apps, their bundle executable Transmission.app/Content/MacOS/Transmission will copy this General.rtf file to ~/Library/kernel_service and execute this “kernel_service” before any user interface appearing.
After unpacking the General.rtf with UPX, we determined that its main behavior is to encrypt the user’s files and hold them for ransom.
Apple has since revoked the abused certificate, and Gatekeeper will now block the malicious installers.
Apple has also updated XProtect signatures to cover the family, and the signature has been automatically updated to all Mac now.
As of March 5, Transmission Project has removed the malicious installers from its website.