Water Sigbin Exploiting Oracle WebLogic Server Flaw

Water Sigbin Exploiting Oracle WebLogic Server Flaw

Water Sigbin (8220 Gang) exploits vulnerabilities (CVE-2017-3506, CVE-2023-21839) in Oracle WebLogic servers to deliver cryptocurrency miners using PowerShell scripts. 

They use a multi-stage loading technique with a .Net Reactor protecting the payload to deploy the PureCrypter loader and XMRig miner, which makes it hard to analyze the code and implement defensive measures. 

Water Sigbin Attack diagram

Water Sigbin exploits CVE-2017-3506 to deploy a PowerShell script that decodes a Base64-encoded payload and then drops a malicious file named wireguard2-3.exe, which impersonates a legitimate VPN application

This dropper is a trojan loader that retrieves, decrypts, maps, and executes a second-stage payload (Zxpus.dll) in memory using reflective DLL injection, allowing the malware to evade detection and carry out malicious activities. 

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Zxpus.dll, a second-stage loader, retrieves a binary named Vewijfiv from its resources, decrypts it using AES with a specified key and IV, and decompresses it using GZip. 

The decompressed payload is then deserialized using protobuf-net, revealing the loader’s configuration, including the process name to be created and the next stage payload in an encrypted format. 

Zxpus.dll creating the cvtres.exe process
Zxpus.dll creating the cvtres.exe process

It then creates a new process named cvtres.exe, injects the decrypted next-stage payload into memory using process injection, and passes the execution to the cvtres.exe process.  

The malware, cvtres.exe, decompresses a DLL file with Gzip and loads it for execution, which is identified as PureCrypter loader version V6.0.7D, which establishes a connection with a command-and-control server and downloads the final malicious payload, which is likely a cryptocurrency miner.  

The PureCrypter loader is a malicious DLL that uses a mutex to ensure only one instance runs by retrieving configuration from its C&C server, including persistence mechanisms and exclusion rules for antivirus

PureCrypter generates a victim ID from system information
PureCrypter generates a victim ID from system information

For persistence, it creates a scheduled task disguised as a synchronized file and another task with a random name to add specific files, and processes to the exclusion list, and then generates a unique identifier for the victim machine based on system information and communicates with the C&C server.  

PureCrypter, a .NET obfuscated loader, downloads and executes various malware, like information stealers and RATs, by using process hollowing to inject the payload into a legitimate process. To evade detection, PureCrypter collects system information using WMI 

queries encrypt it with TripleDES and send it to the C&C server. 

XMRig login request
XMRig login request

According to Trend Micro, the C&C server responds with an encrypted XMRig mining configuration, which is stored in the registry. 

PureCrypter then downloads the XMRig payload (plugin3.dll), decrypts it, injects it into a newly created process (AddinProcess.exe), and starts mining for the XMRig mining pool at the address using the wallet address ZEPHYR2xf9vMHptpxP6VY4hHwTe94b2L5SGyp9Czg57U8DwRT3RQvDd37eyKxoFJUYJvP5ivBbiFCAMyaKWUe9aPZzuNoDXYTtj2Z.c4k.  

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Author: Aman Mishra