CrySiS targets Windows OS and is distributed as malicious attachments in spam emails and disguised as installation files for legitimate software. Once it infects a system, it creates registry entries to maintain persistence and encrypts all file types, with the exception of system and malware files, on fixed, removable, and network drives. CrySiS then drops a ransom note on the desktop for the victim, providing two email addresses the victim can use to contact the attackers. The ransom demand is between 0.79 and 1.18 Bitcoin.
UPDATE 11/14/2016: The master decryption keys for the CrySiS ransomware variant have been released to the public.
UPDATE 11/29/2016: A new version of CrySiS has been discovered appending encrypted file names with .dharma or .wallet. This version cannot be decrypted at the time of this update.
UPDATE 3/2/2017: The master keys for the Dharma version of CrySiS have been released. Kaspersky used these keys to add decryption functionality for Dharma in the Rakhni Decryptor available on NoMoreRansom.org.
UPDATE 4/15/2017: A new version of CrySiS appends .onion to encrypted file names.
- We Live Security provides more information about CrySiS here.
- Kaspersky’s free decryption tool, RakhniDecryptor, can now decrypt CrySiS.
ESET also provides a free decryption tool for CrySiS, available here.