CLNTEND (Backdoor) – Malware

Overview

CLNTEND is a recently discovered remote access tool (RAT) that has been observed in targeted cyberattacks against military and industrial sectors. It is part of a sophisticated malware toolkit employed by threat actors seeking to infiltrate and maintain control over victim systems. Unlike more traditional malware, CLNTEND is designed with advanced functionalities that enable attackers to execute remote commands, perform system reconnaissance, and move laterally within compromised networks. Its modular nature allows it to adapt to different attack scenarios, making it a versatile and potent weapon for cybercriminals and state-sponsored threat groups alike.

The primary functionality of CLNTEND is its ability to establish and maintain remote access to compromised systems. This RAT communicates over a variety of network protocols, ensuring that it can bypass network defenses and remain persistent even when the environment undergoes changes. Once installed, CLNTEND allows attackers to remotely control the victim’s machine, access sensitive information, and execute additional malicious payloads. The tool also facilitates the collection of system data, which can be used for further exploitation or as part of larger espionage operations.

Targets

Information

How they operate

Initial Access and Execution:

CLNTEND often gains entry into a target system through remote desktop services, such as UltraVNC. The malware is typically delivered via an external compromise, often using social engineering or exploiting vulnerabilities within exposed remote services. Upon successful compromise, the malware runs in the background without raising suspicion, initiating its core functionalities. One of the primary methods of execution is leveraging legitimate remote desktop applications to run arbitrary code on the infected system. This execution stage allows the malware to establish a foothold within the target network.

Privilege Escalation and Persistence:

Once executed, CLNTEND seeks to escalate its privileges to gain broader access to the infected system. It often employs techniques such as credential dumping to obtain higher privileges or utilize stolen credentials for lateral movement across the network. Privilege escalation is critical for gaining full control of the system, as it allows CLNTEND to interact with higher-level system processes and sensitive files. To ensure persistence, the malware modifies system settings, such as creating new services that enable it to execute automatically during system boot-ups. This persistence mechanism guarantees that the malware remains active even after a reboot or user intervention.

Evasion and Anti-Analysis Techniques:

One of the most sophisticated aspects of CLNTEND is its ability to evade detection by antivirus tools and other security monitoring systems. The malware employs various techniques to obscure its activities, such as clearing logs and deleting traces of its presence. Anti-analysis capabilities are also a key feature, as CLNTEND can check for debugging environments or sandboxing tools before activating its full set of malicious activities. It may hook critical application programming interfaces (APIs), such as GetProcAddress, to alter the execution flow and prevent detection by traditional security measures.

Lateral Movement and Data Collection:

After securing elevated privileges, CLNTEND can move laterally across the network to infect additional machines. Using its remote desktop functionality, the malware can establish connections with other systems and propagate further within the network. During this stage, it collects valuable information, such as system configurations, user credentials, and other sensitive data. This collected data is then sent back to the attacker via command and control (C2) channels. The malware’s ability to continuously collect and exfiltrate information makes it a powerful tool for cyber espionage.

Command and Control Communication:

CLNTEND operates through an established command and control (C2) channel, enabling remote operators to interact with the infected system. Communication with the C2 server allows the attackers to issue commands, deliver additional payloads, or exfiltrate sensitive data. CLNTEND supports various communication protocols, ensuring its ability to adapt to different network environments. It can blend into regular network traffic, making it difficult to identify without deep packet inspection or behavioral analysis.

Conclusion:

CLNTEND is a highly effective and adaptable malware that leverages remote access capabilities to infiltrate, control, and exfiltrate sensitive data from compromised systems. Its ability to evade detection, escalate privileges, and maintain persistence makes it a dangerous tool in the hands of cybercriminals or state-backed threat actors. By understanding its technical operation, cybersecurity professionals can better defend against such threats, implementing network monitoring, endpoint protection, and privilege management to mitigate the risk posed by CLNTEND and similar malware strains.

MITRE Tactics and Techniques

Initial Access (T1071: Application Layer Protocol): CLNTEND often gains initial access to victim systems by exploiting legitimate applications and remote desktop protocols, such as UltraVNC, which is used for remote access to the victim’s machine. This tactic allows the malware to bypass network defenses and gain entry into a target environment.

Execution (T1059: Command and Scripting Interpreter): CLNTEND can execute commands on the infected system through its remote access capabilities. It can execute malicious scripts or commands by using the system’s command shell to run malicious payloads or interact with the operating system.

Persistence (T1050: New Service): The malware may establish persistence on the infected system by creating new services that automatically run the malware during system boot-up. This ensures that CLNTEND remains active even after the system reboots.

Privilege Escalation (T1075: Pass the Hash): CLNTEND has been observed using privilege escalation techniques to escalate its privileges within the victim’s environment. It may leverage credentials or bypass security mechanisms to gain higher levels of access, allowing for further exploitation of the system.

Defense Evasion (T1070: Indicator Removal on Host): CLNTEND employs a variety of techniques to evade detection and remove traces of its activities from the victim system. This includes clearing logs and deleting specific files associated with the malware to avoid detection by antivirus and security monitoring tools.

Credential Dumping (T1003: OS Credential Dumping): During the post-exploitation phase, CLNTEND can dump credentials from the infected system, including local account passwords, to facilitate further lateral movement or to escalate privileges.

Lateral Movement (T1021: Remote Services): CLNTEND allows threat actors to move laterally across the network by leveraging its remote access capabilities. This enables attackers to compromise additional systems and expand their foothold within the network.

Collection (T1119: Automated Collection): The malware is capable of collecting sensitive information from the infected systems, such as IP addresses, MAC addresses, and system configurations, to exfiltrate or use for further exploitation.

Command and Control (T1071: Application Layer Protocol): CLNTEND establishes communication with its command and control (C2) server using various application layer protocols. This allows the attackers to remotely control the infected system and send further commands or additional payloads.

Exfiltration (T1041: Exfiltration Over Command and Control Channel): Once data has been collected, CLNTEND may exfiltrate sensitive information back to the attacker’s command and control infrastructure. This exfiltration can occur through the same communication channels used for command and control, ensuring persistence and covert data extraction.

References

• TIDRONE Targets Military and Satellite Industries in Taiwan