File and Directory Discovery
Adversaries may enumerate files and directories or may search in specific locations of a host or network share for certain information within a file system.
Example utilities used to obtain this information are
tree.  Custom tools may also be used to gather file and directory information and interact with the Windows API.
Mac and Linux
In Mac and Linux, this kind of discovery is accomplished with the
admin@338 actors used the following commands after exploiting a machine with LOWBALL malware to obtain information about files and directories:
Backdoor.Oldrea collects information about available drives, default browser, desktop file list, My Documents, Internet history, program files, and root of available drives. It also searches for ICS-related software files.
BlackEnergy gathers a list of installed apps from the uninstall program Registry. It also gathers registered mail, browser, and instant messaging clients from the Registry. BlackEnergy has searched for given file types.
Cardinal RAT checks its current working directory upon execution and also contains watchdog functionality that ensures its executable is located in the correct path (else it will rewrite the payload).
CrossRAT can list all files on a system.
A variant of Elise executes
GeminiDuke collects information from the victim, including installed drivers, programs previously executed by users, programs and services configured to automatically run at startup, files and folders present in any user's home folder, files and folders present in any user's My Documents, programs installed to the Program Files folder, and recently accessed files, folders, and programs.
Several Lazarus Group malware samples use a common function to identify target files by their extension. Lazarus Group malware families can also enumerate files and directories, including a Destover-like variant that lists files and gathers information for all drives.
NETEAGLE allows adversaries to enumerate and modify the infected host's file system. It supports searching for directories, creating directories, listing directory contents, reading and writing to files, retrieving file attributes, and retrieving volume information.
Sowbug identified and extracted all Word documents on a server by using a command containing * .doc and *.docx. The actors also searched for documents based on a specific date range and attempted to identify all installed software on a victim.
TrickBot searches the system for all of the following file extensions: .avi, .mov, .mkv, .mpeg, .mpeg4, .mp4, .mp3, .wav, .ogg, .jpeg, .jpg, .png, .bmp, .gif, .tiff, .ico, .xlsx, and .zip. It can also obtain browsing history, cookies, and plug-in information.
WannaCry searches for variety of user files by file extension before encrypting them using RSA and AES, including Office, PDF, image, audio, video, source code, archive/compression format, and key and certificate files.
WinMM sets a WH_CBT Windows hook to search for and capture files on the victim.
File system activity is a common part of an operating system, so it is unlikely that mitigation would be appropriate for this technique. It may still be beneficial to identify and block unnecessary system utilities or potentially malicious software by using whitelisting  tools, like AppLocker,   or Software Restriction Policies  where appropriate. 
System and network discovery techniques normally occur throughout an operation as an adversary learns the environment. Data and events should not be viewed in isolation, but as part of a chain of behavior that could lead to other activities, such as Collection and Exfiltration, based on the information obtained.
Monitor processes and command-line arguments for actions that could be taken to gather system and network information. Remote access tools with built-in features may interact directly with the Windows API to gather information. Information may also be acquired through Windows system management tools such as Windows Management Instrumentation and PowerShell.
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