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.  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 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 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.

Source: GBHackers