Command Obfuscation

What the technique is

Adversaries may obfuscate content during command execution to impede detection. Command-line obfuscation is a method of making strings and patterns within commands and scripts more difficult to signature and analyze. This type of obfuscation can be included within commands executed by delivered payloads (e.g., Phishing and Drive-by Compromise) or interactively via Command and Scripting Interpreter. For example, adversaries may abuse syntax that utilizes various symbols and escape characters (such as spacing, ^, +. $, and %) to make commands difficult to analyze while maintaining the same intended functionality. Many languages support built-in obfuscation in the form of base64 or URL encoding. Adversaries may also manually implement command obfuscation via string splitting (“Wor”+“d.Application”), order and casing of characters (rev <<<'dwssap/cte/ tac'), globing (mkdir -p '/tmp/:&$NiA'), as well as various tricks involving passing strings through tokens/environment variables/input streams. Adversaries may also use tricks such as directory traversals to obfuscate references to the binary being invoked by a command (C:\voi\pcw\..\..\Windows\tei\qs\k\..\..\..\system32\erool\..\wbem\wg\je\..\..\wmic.exe shadowcopy delete). Tools such as Invoke-Obfuscation and Invoke-DOSfucation have also been used to obfuscate commands.

What MITRE says you would watch

• AN1394

  Detection of command-line activity exhibiting syntactic obfuscation patterns, such as excessive escape characters, base64 encoding, command concatenation, or outlier command length and entropy.

• AN1395

  Detection of shell commands that leverage encoded execution, command chaining, excessive piping, or unusual token patterns indicative of obfuscation.

• AN1396

  Detection of obfuscated commands via shell, osascript, or AppleScript interpreters using unusual tokens, encoding, variable substitution, or runtime string reconstruction.