OceanLotus APT Hackers Group using Steganography to Launch an Encrypted Malware Payload via .png Image File

by chebbi abir

A Well-known APT Group OceanLotus leveraging a steganography method to hide the encrypted malware payload within a .png image file to infect the targeted system.

OceanLotus group known for Multiple attack campaigns around the globe, the threat actor group targets private sectors across multiple industries, foreign governments.

Steganography, a method used by attackers to hide the malicious code within the image that is mainly employed by exploit kits to hide the malvertising traffic.

Attackers using 2 different backdoors within this campaign, both are distributing the via encrypted and an obfuscated loader .

In order to increase the infection success ratio, APT Groups are heavily investing to develop the highly sophisticated hacking tools.

First steganography loader mimics the McAfee’s McVsoCfg DLL and drops in to the targeted system along with legitimate “On Demand Scanner” executable.

In this case, attackers launching this first loader via a separate .png image file which is not a malicious one, but the PNG file was abused and load the payload using steganography which utilizes the least significant bits of each pixel’s color code to store hidden information.

Attackers made up this payload that encrypted with AES128 and further obfuscated with XOR to bypass the steganography detection tools.

Second steganography loader using same payload extraction routine as the previous loader but it differs from decryption routine and anti-analysis technique and this loader is an updated version of Remy backdoor.

Second payload contains some of the serious future including Side-loaded DLL, Anti-debugging/anti-sandboxing, AES128 implementation from Crypto++ library for payload decryption.

Image containing encoded payload 

Loader Launching the Backdoor

Attackers launching the final backdoor from the Launcher DLL that contains an encrypted backdoor in its resources along with one or more C2 communication modules.

Decoding Process

In this case, Backdoor DLL and the C2 communication DLLs are heavily obfuscated using tons of junk code that makes more difficult for debugging and static analysis.

According to cylance report , In addition to Denes and Remy backdoors, at least two different communication modules were observed with different versions of this launcher – DNSProvider and HTTPProv

The launcher binary, which contains the final backdoor, is RC4 encrypted and wrapped in a layer of obfuscated shellcode.

Finally shellcode execute and launch the C2 communication module resources that compressed with LZMA.

Later the malware communicates with the with an attacker to receive the various commands to steal the various sensitive information. You can Also read the complete technical analysis report here.


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