Researchers from Trend Micro have uncovered BatCloak, a fully undetectable (FUD) malware obfuscation engine used by threat actors to stealthily distribute malware since September 2022.
Through their analysis, they found that the samples demonstrated an impressive ability to consistently evade anti-malware solutions, with 80% of the analyzed samples showing zero detections by security solutions. The average detection rate for the entire sample set was less than one, highlighting the effectiveness of BatCloak in bypassing defenses.
BatCloak is part of a larger FUD builder called Jlaive, which emerged in 2022. The analysis of the Jlaive repository revealed the developer’s efforts in FUD technologies, including the use of AES encryption and techniques to bypass anti-malware scan interfaces. Although the original repository was taken down, modified versions and clones have surfaced, with threat actors offering Jlaive as a one-time service for purchase instead of a subscription model.
Despite the removal of many repositories hosting modified or cloned versions of Jlaive from platforms like GitHub and GitLab, threat actors continue to upload the code.
Additionally, some development teams have even ported the code to other languages such as Rust. Jlaive utilizes a modified version of Nettitudes RunPE reflective loader to maintain the payload in memory and execute multiple portable executables (PEs) within the same process.
The BatCloak engine, which serves as the core component of Jlaive’s obfuscation algorithm, includes LineObfuscation.cs and FileObfuscation.cs. The final payload is packed using a C# loader, a PowerShell loader, and a batch loader. The latest version of BatCloak, named ScrubCrypt, has been identified by Fortinet FortiGuard Labs and has undergone testing on various popular malware strains.
The evolution of BatCloak demonstrates its adaptability and highlights the development of FUD batch obfuscators, posing significant challenges to cybersecurity defenses.
