Rewterz Threat Alert – Chinese Cyber Espionage Group BlackTech Using BendyBear Shellcode

Severity

High

Analysis Summary

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:

• Transmits payloads in modified RC4-encrypted chunks. This hardens the encryption of the network communication, as a single RC4 key will not decrypt the entire payload.
• Attempts to remain hidden from cybersecurity analysis by explicitly checking its environment for signs of debugging.
• Leverages existing Windows registry key that is enabled by default in Windows 10 to store configuration data.
• Clears the host’s DNS cache every time it attempts to connect to its C2 server, thereby requiring that the host resolve the current IP address for the malicious C2 domain each time.
• Generates unique session keys for each connection to the C2 server.
• Obscures its connection protocol by connecting to the C2 server over a common port (443), thereby blending in with normal SSL network traffic.
• Employs polymorphic code, changing its runtime footprint during code execution to thwart memory analysis and evade signaturing.
• Encrypts or decrypts function blocks (code blocks) during runtime, as needed, to evade detection.
• Uses position independent code (PIC) to throw off static analysis tools.

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. 

Impact

• Detection Evasion
• Code Execution
• Information Disclosure
• Data Exfiltration

Indicators of Compromise

Domain Name

• wg1[.]inkeslive[.]com
• web2008[.]rutentw[.]com

MD5

• 3baab75ef08834d0fdb24369e0fd7c7a
• 633ca057be3189b5da3678849aa5d9ce
• 26e0b9a97a9448f2c6cccfd1003e0cb0
• 05f34b09b28e771c99b8578f8a4324ce
• 386091b299cfbe9b95034b21be7aa44c
• 2a321465999f74ac4055e83e58be2624

SHA-256

• 49901034216a16cfd05c613f438eccee4a7bf6079a7988b3e7094d9498379558
• 5d1414b47d88e95ae6612d3fc211c29b35cc5db4a8a992f5e27cff5203ebf44b
• 9880ba4f93cade2f6bbb4cc8efdcf087e8ac51b5c209ee32ad8134eb87ef70e1
• 682122f34027e3f8025928d446989b02952449f5e5930c2670f8f789f41573ff
• 2a09ec2d6edadd06e18c841e0ed794ba3eeb21818476f75ccc0e5d40e08eac80
• 76ef704d21fbaaceca8a131429ccfb9f5de3d8f43a160ddd281ffeafc391eb98
• 64CC899EC85F612270FCFB120A4C80D52D78E68B05CAF1014D2FE06522F1E2D0

SHA1

• 7fd541d4b34c38352e36ea1081041d9390f4789e
• d35224bb1c8007082dd1d53f5811d1bed53317f9
• 2b770e58af6a26879be51f45ee279490fa0fd3b5
• d5732316e2d3f113960a577b6a0496c99020afb2
• 5546573eade55c6361d2ef8a456f4d82087afafc
• 2288c68a3534dac16f67fc3af1b4a68dfcda5baf

Remediation

• Block the threat indicators at their respective controls.
• Search for IoCs in your environment.