CSHARP-STREAMER (Trojan) – Malware

Overview

In the ever-evolving landscape of cybersecurity threats, the csharp-streamer Remote Access Trojan (RAT) presents a sophisticated and multifaceted challenge for defenders. Discovered in December 2023, this malware exemplifies the increasing complexity of modern threats and highlights the ingenious methods employed by cybercriminals to evade detection and maintain persistent access to compromised systems. Written in C#, csharp-streamer demonstrates a remarkable blend of technical sophistication and obfuscation techniques, making it a formidable adversary in the realm of cyber threats.

Targets

Information

How they operate

At its core, csharp-streamer leverages a PowerShell stager to deploy its payload, employing heavily obfuscated scripts to bypass security mechanisms such as the Anti-Malware Scan Interface (AMSI). The initial stage involves an intricate PowerShell script that obscures its true intentions through complex arithmetic and dead code. Once the script is executed, it dynamically decrypts and loads the RAT payload from a remote server, masquerading as a benign file to evade detection. This sophisticated delivery mechanism underscores the malware’s adaptability and the challenges it poses for traditional detection methods.

Once installed, csharp-streamer offers an extensive array of capabilities that reflect its well-planned design for maintaining control over compromised systems. Its features include advanced keylogging, file exfiltration, network reconnaissance, and remote command execution, facilitated through a command-line interface and various custom protocols. The RAT’s reliance on third-party libraries and open-source components further enhances its functionality while also posing unique challenges for analysts attempting to dissect and understand its operations. The malware’s ability to execute arbitrary .NET assemblies and interact with system components underscores its potential for significant disruption and data compromise.

In addition to its technical sophistication, csharp-streamer’s operational tactics reveal a deliberate effort to evade detection and establish persistent access. Its use of encrypted communication channels, dynamic code execution, and a lack of built-in persistence mechanisms illustrate the malware authors’ intent to create a stealthy and resilient threat. As cybersecurity professionals continue to contend with increasingly sophisticated threats, csharp-streamer serves as a compelling case study of how modern malware can exploit technical intricacies and evasion techniques to achieve its malicious objectives.

MITRE Tactics and Techniques

Initial Access:

Phishing (T1566): The malware may use phishing emails or malicious attachments to deliver the initial PowerShell stager.
Drive-by Compromise (T1189): The malware might exploit vulnerabilities in web browsers or plugins to deliver the payload.

Execution:

PowerShell (T1059.001): The malware uses heavily obfuscated PowerShell scripts to execute its payload, a technique employed to bypass security controls and execute malicious code.
Command-Line Interface (T1059.003): The RAT might use command-line interfaces to execute its commands and maintain control over the infected system.

Persistence:

Registry Run Keys/Startup Folder (T1547.001): The RAT could be configured to modify registry keys or startup folders to maintain persistence on the infected system.

Privilege Escalation:

Exploitation of Vulnerabilities (T1203): The malware may exploit system vulnerabilities to gain higher privileges and expand its access.

Defense Evasion:

Obfuscated Files or Information (T1027): csharp-streamer uses obfuscation techniques in its PowerShell scripts and payloads to evade detection.
Code Signing (T1116): The RAT might employ code-signing techniques to appear as a legitimate application.

Credential Access:

Keylogging (T1056.001): csharp-streamer includes keylogging capabilities to capture user credentials and other sensitive information.
Credential Dumping (T1003): The RAT may attempt to dump credentials from the system to further compromise accounts.

Discovery:

System Information Discovery (T1082): The malware can gather information about the system and network to identify valuable targets or opportunities for further exploitation.

Lateral Movement:

Remote File Copy (T1105): The RAT might facilitate lateral movement by copying files or scripts to other systems in the network.

References:

• The csharp-streamer RAT