Selective Exclusion

What the technique is

Adversaries may intentionally exclude certain files, folders, directories, file types, or system components from encryption or tampering during a ransomware or malicious payload execution. Some file extensions that adversaries may avoid encrypting include.dll,.exe, and.lnk. Adversaries may perform this behavior to avoid alerting users, to evade detection by security tools and analysts, or, in the case of ransomware, to ensure that the system remains operational enough to deliver the ransom notice. Exclusions may target files and components whose corruption would cause instability, break core services, or immediately expose the attack. By carefully avoiding these areas, adversaries maintain system responsiveness while minimizing indicators that could trigger alarms or otherwise inhibit achieving their goals.

What MITRE says you would watch

• AN2030

  A process with no prior history or outside of known whitelisted tools initiates file or registry modifications to configure exclusion rules for antivirus, backup, or file-handling systems. Or a file system enumeration for specific file names andcritical extensions like.dll,.exe,.sys, or specific directories such as 'Program Files' or security tool paths or system component discovery for the exclusion of the files or components.