New BendyBear APT Malware Gets Linked To Chinese Hacking Group

Unit 42 researchers today have shared info on a new polymorphic and “highly sophisticated” malware dubbed BendyBear, linked to a hacking group with known ties to the Chinese government.

BendyBear is also “one of the most sophisticated, well-engineered and difficult-to-detect samples of shellcode employed by an Advanced Persistent Threat (APT)” according to a Unit 42 report published earlier today.

Although discovered last year, in August 2020, there is no information on the infection vector used to deploy it on targeted systems or any potential victims.

The malware has features and behavior that strongly resemble those of the WaterBear malware family, active since at least as early 2009.

WaterBear is connected to BlackTech, a cyberespionage group linked by threat researchers to the Chinese government.

This nation-state hacker group is focused on information theft and is also suspected to have coordinated recent attacks targeting several East Asian government organizations.

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Malware features and capabilities

This shellcode’s only function is to be used to download other malicious payloads from attacker-controlled command and control (C2) servers.

Cyberspies who use BendyBear in their operations will load it onto compromised devices immediately after gaining access to the machine following exploitation.

“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,” Unit 42 said.

Among BendyBear’s long list of features and capabilities, Unit 42 says 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.

Due to the features such as signature block verification and the use of anti-analysis techniques, it’s fairly obvious that BendyBear’s developers are focused on making it a stealthy and detection-evasion malware.

Furthermore, its creators show a “high level of technical sophistication” based on the use of byte manipulations and custom cryptographic routines.

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More technical details on the BendyBear shellcode, indicators of compromise, and shellcode proof of concept are available in Unit 42’s report.