Ingress Tool Transfer

What the technique is

Adversaries may transfer tools or other files from an external system into a compromised environment. Tools or files may be copied from an external adversary-controlled system to the victim network through the command and control channel or through alternate protocols such as ftp. Once present, adversaries may also transfer/spread tools between victim devices within a compromised environment (i.e. Lateral Tool Transfer). On Windows, adversaries may use various utilities to download tools, such as copy, finger, certutil, and PowerShell commands such as IEX(New-Object Net.WebClient).downloadString() and Invoke-WebRequest. On Linux and macOS systems, a variety of utilities also exist, such as curl, scp, sftp, tftp, rsync, finger, and wget. A number of these tools, such as wget, curl, and scp, also exist on ESXi. After downloading a file, a threat actor may attempt to verify its integrity by checking its hash value (e.g., via certutil -hashfile). Adversaries may also abuse installers and package managers, such as yum or winget, to download tools to victim hosts. Adversaries have also abused file application features, such as the Windows search-ms protocol handler, to deliver malicious files to victims through remote file searches invoked by User Execution (typically after interacting with Phishing lures). […]

What MITRE says you would watch

• AN0165

  Unusual or uncommon processes initiate network connections to external destinations followed by file creation (tools downloaded).

• AN0166

  Shell-based tools (curl, wget, scp) initiate connections to external domains followed by creation of executable files on disk.

• AN0167

  Process execution of curl or wget followed by a network connection and a file created in temporary or user-specific directories.