Steganography

What the technique is

Adversaries may use steganography techniques in order to prevent the detection of hidden information. Steganographic techniques can be used to hide data in digital media such as images, audio tracks, video clips, or text files. Duqu was an early example of malware that used steganography. It encrypted the gathered information from a victim's system and hid it within an image before exfiltrating the image to a C2 server. By the end of 2017, a threat group used Invoke-PSImage to hide PowerShell commands in an image file (.png) and execute the code on a victim's system. In this particular case the PowerShell code downloaded another obfuscated script to gather intelligence from the victim's machine and communicate it back to the adversary.

What MITRE says you would watch

• AN0331

  Detects execution of image viewers or PowerShell scripts accessing or decoding files with mismatched MIME headers or embedded script-like byte patterns; often correlated with suspicious parent-child process lineage and outbound connections.

• AN0332

  Detects access to media files followed by execution of scripts (bash, Python, etc.) referencing those same files, or outbound traffic triggered shortly after file read. Correlates unusual use of tools like steghide, exiftool, or image libraries.

• AN0333

  Detects manipulation of PNG, JPG, or GIF files by user-initiated scripts followed by script execution or exfiltration behavior, especially from osascript, python, or bash, in combination with LaunchAgent persistence or curl activity.