Adversaries may encrypt data on target systems or on large numbers of systems in a network to interrupt availability to system and network resources. They can attempt to render stored data inaccessible by encrypting files or data on local and remote drives and withholding access to a decryption key. This may be done in order to extract monetary compensation from a victim in exchange for decryption or a decryption key (ransomware) or to render data permanently inaccessible in cases where the key is not saved or transmitted. In the case of ransomware, it is typical that common user files like Office documents, PDFs, images, videos, audio, text, and source code files will be encrypted. In some cases, adversaries may encrypt critical system files, disk partitions, and the MBR.
To maximize impact on the target organization, malware designed for encrypting data may have worm-like features to propagate across a network by leveraging other attack techniques like Valid Accounts, OS Credential Dumping, and SMB/Windows Admin Shares.
In cloud environments, storage objects within compromised accounts may also be encrypted.
Conti can use
Maze has disrupted systems by encrypting files on targeted machines, claiming to decrypt files if a ransom payment is made. Maze has used the ChaCha algorithm, based on Salsa20, and an RSA algorithm to encrypt files.
Ryuk has used a combination of symmetric (AES) and asymmetric (RSA) encryption to encrypt files. Files have been encrypted with their own AES key and given a file extension of .RYK. Encrypted directories have had a ransom note of RyukReadMe.txt written to the directory.
XCSSET performs AES-CBC encryption on files under
|M1040||Behavior Prevention on Endpoint||
On Windows 10, enable cloud-delivered protection and Attack Surface Reduction (ASR) rules to block the execution of files that resemble ransomware. 
Consider implementing IT disaster recovery plans that contain procedures for regularly taking and testing data backups that can be used to restore organizational data. Ensure backups are stored off system and is protected from common methods adversaries may use to gain access and destroy the backups to prevent recovery. Consider enabling versioning in cloud environments to maintain backup copies of storage objects.
|ID||Data Source||Data Component|
|DS0010||Cloud Storage||Cloud Storage Metadata|
|Cloud Storage Modification|
Use process monitoring to monitor the execution and command line parameters of binaries involved in data destruction activity, such as vssadmin, wbadmin, and bcdedit. Monitor for the creation of suspicious files as well as unusual file modification activity. In particular, look for large quantities of file modifications in user directories.
In some cases, monitoring for unusual kernel driver installation activity can aid in detection.
In cloud environments, monitor for events that indicate storage objects have been anomalously replaced by copies.