A cyber espionage group BlackTech was previously known for WaterBear, a multifaceted, stage-two implant, capable of file transfer, shell access, screen capture and much more. Threat research community suspects the group to have ties to the Chinese government, and is believed to be responsible for recent attacks against several East Asian government organizations. Due to the similarities with WaterBear, a new Chinese shellcode “BendyBear.” has been associated with BlackTech as well. It’s one of the most sophisticated, well-engineered and difficult-to-detect samples of shellcode employed by an Advanced Persistent Threat (APT). The BendyBear sample is likely a x64 shellcode for a stage-zero implant whose sole function is to download a more robust implant from a command and control (C2) server. Shellcode, despite its name, is used to describe the small piece of code loaded onto the target immediately following exploitation, regardless of whether or not it actually spawns a command shell. At 10,000+ bytes, BendyBear is noticeably larger than most, and uses its size to implement advanced features and anti-analysis techniques, such as modified RC4 encryption, signature block verification, and polymorphic code. A common attack vector has not been identified so far.
BendyBear is unique in that it:
The shellcode is considered to be a stager, or downloader, whose function is to download an implant from a C2 server. During execution, the code employs byte randomization to obscure its behavior.