Obfuscated Files or Information

What the technique is

Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit. This is common behavior that can be used across different platforms and the network to evade defenses. Payloads may be compressed, archived, or encrypted in order to avoid detection. These payloads may be used during Initial Access or later to mitigate detection. Sometimes a user's action may be required to open and Deobfuscate/Decode Files or Information for User Execution. The user may also be required to input a password to open a password protected compressed/encrypted file that was provided by the adversary. Adversaries may also use compressed or archived scripts, such as JavaScript. Portions of files can also be encoded to hide the plain-text strings that would otherwise help defenders with discovery. Payloads may also be split into separate, seemingly benign files that only reveal malicious functionality when reassembled. Adversaries may also abuse Command Obfuscation to obscure commands executed from payloads or directly via Command and Scripting Interpreter. Environment variables, aliases, characters, and other platform/language specific semantics can be used to evade signature based detections and application control mechanisms.

What MITRE says you would watch

• AN1064

  Correlates script execution or suspicious parent processes with creation or modification of encoded, compressed, or encrypted file formats (e.g.,.zip,.7z,.enc) and abnormal command-line syntax or PowerShell obfuscation.

• AN1065

  Detects use of gzip, base64, tar, or openssl in scripts or commands that encode/encrypt files after file staging or system enumeration.

• AN1066

  Monitors use of archive or encryption tools (zip, openssl) tied to user-scripted activity or binaries writing encoded payloads under /Users or /Volumes.