Rewterz Threat Alert – APT Using Steganography to Spread CobaltStrike

Severity

High

Analysis Summary

A new strand of malware uses Word files with macros to download a PowerShell script from GitHub. This PowerShell script further downloads a legitimate image file from image hosting service Imgur to decode a Cobalt Strike script on Windows systems. Multiple researchers have potentially linked this strain to the APT group MuddyWater (aka SeedWorm) that mainly targets Middle Eastern entities. This new macro-based malware that is evasive and spawns payload in multifaceted steps, looks a lot like MuddyWater and ships as an embedded macro within a legacy Microsoft Word (*.doc) file. The macro embedded in the word document leads to a PowerShell script from GitHub that fetches an image file from Imgur. Using Steganography, tools like Invoke-PSImage encode a PowerShell script within the pixels of a PNG file and generate a one-line command to execute the payload. The payload calculation algorithm runs a foreach loop to iterate over a set of pixel values within the PNG image and performs specific arithmetic operations to obtain functional ASCII commands. The decoded script obtained from manipulating the PNG’s pixel values is a Cobalt Strike script. It is used to deploy “beacons” on compromised devices to remotely create shells, execute PowerShell scripts, perform privilege escalation, or spawn a new session to create a listener on the victim system. The payload, however, indeed contacts the command-and-control (C2) server via a WinINet module to receive further instructions.

Impact

• Remote Code Execution
• Privilege Escalation
• Unauthorized Access
• Data Exfiltration

Indicators of Compromise

Domain Name

• Mazzion1234-44451[.]portmap[.]host

MD5

• 97b5ca432a34b919a59fe8bc8e213fc3
• a9506c371418969ea5084b00db54573b

SHA-256

• d1c7a7511bd09b53c651f8ccc43e9c36ba80265ba11164f88d6863f0832d8f81
• ed93ce9f84dbea3c070b8e03b82b95eb0944c44c6444d967820a890e8218b866

SHA1

• 6774f7b5e533a4158b2b2375cf06fbc95e434526
• 1fb678ab15f3c311d7189d4c80bc7c91bc360e49

Remediation

• Block the threat indicators at their respective controls.
• Do not download files attached in untrusted emails or from random sources on the internet.