High
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.