Cobalt Strike (Dropper) – Malware

Overview

Cobalt Strike is a sophisticated and versatile commercial penetration testing tool that has gained notoriety for its use in both legitimate cybersecurity assessments and malicious cyber activities. Developed by Strategic Cyber LLC, Cobalt Strike is renowned for its core component, the Beacon agent, which is instrumental in facilitating complex cyber operations. This tool allows security professionals to simulate advanced persistent threats (APTs) and assess the resilience of networks and systems, but its capabilities have also made it a favored choice among cybercriminals and state-sponsored threat actors.

Beacon, the centerpiece of Cobalt Strike, is a powerful in-memory agent that enables a wide range of functionalities crucial for both penetration testing and adversarial activities. Its features include command execution, keylogging, file transfer, SOCKS proxying, and lateral movement. What sets Beacon apart is its file-less operation, which allows it to load directly into the memory of a compromised process, thereby avoiding detection by traditional file-based security solutions. This stealthy nature, combined with support for multiple command and control (C2) channels such as HTTP, HTTPS, DNS, and TCP, makes Beacon exceptionally difficult to detect and defend against.

The tool’s flexibility and robustness have attracted various threat groups, including notorious advanced persistent threats (APTs) and cybercriminal organizations. Groups such as APT 29, APT32, and FIN7 have leveraged Cobalt Strike in their operations, utilizing its capabilities to conduct sophisticated cyberattacks, data exfiltration, and network intrusions. The broad adoption of Cobalt Strike by both red team professionals and adversarial actors underscores its dual-edged nature—while it serves as a valuable resource for enhancing cybersecurity, it also poses significant risks when used with malicious intent.

Targets

Government Agencies: Many state-sponsored threat groups use Cobalt Strike to target government organizations to steal sensitive information and conduct espionage.

Financial Institutions: Banks and financial services companies are targeted for financial gain and to access sensitive financial data.

Corporate Enterprises: Large corporations across various industries are targeted for intellectual property theft, espionage, and disruption.

Healthcare Organizations: Medical institutions and organizations may be targeted for sensitive patient data and research information.

Educational Institutions: Universities and research institutions can be targets for their valuable research data and intellectual property.

Critical Infrastructure: Entities involved in critical infrastructure, such as utilities and transportation, are targeted to disrupt operations and cause broader impacts.

How they operate

At its core, Cobalt Strike employs a versatile agent known as Beacon, which is designed to perform a wide range of actions on compromised systems. Beacon’s functionality and stealth capabilities make it a powerful tool for both legitimate cybersecurity assessments and advanced adversarial operations.

The Beacon agent operates primarily in-memory, meaning that it executes its payload directly from memory without touching the disk. This fileless operation significantly reduces the chances of detection by traditional file-based security solutions. Beacon can be deployed via multiple infection vectors, such as exploiting vulnerabilities in software or using social engineering tactics to trick users into executing malicious payloads. Once deployed, Beacon establishes a command and control (C2) channel with the attacker’s server, using various protocols including HTTP, HTTPS, DNS, and TCP. This flexibility in communication methods helps Beacon evade network defenses and maintain persistence.

Once activated, Beacon provides attackers with a comprehensive suite of functionalities. It allows for remote command execution, enabling attackers to run arbitrary commands on the compromised system. This includes advanced features such as keylogging, which captures keystrokes to extract sensitive information, and file transfer capabilities, which facilitate the movement of files to and from the infected machine. Beacon also supports SOCKS proxying, allowing attackers to route traffic through the compromised system, further masking their activities. Additionally, it provides tools for privilege escalation and lateral movement, enabling attackers to escalate their access and spread through the network to other systems.

To further enhance its stealth and effectiveness, Beacon incorporates several evasion techniques. It employs obfuscation to hide its code and activities, making it harder for security tools to detect and analyze. Beacon can also use techniques such as process injection and reflective DLL injection to run malicious code in the context of legitimate processes, further avoiding detection. Additionally, Cobalt Strike includes a toolkit called Artifact Kit, which helps in developing shellcode loaders that can be used to deliver Beacon in various ways. These capabilities make Cobalt Strike a formidable tool in the arsenal of both penetration testers and malicious actors, highlighting the importance of advanced detection and response measures in modern cybersecurity.

MITRE Tactics and Techniques

Initial Access:

Exploit Public-Facing Application (T1190): Exploits vulnerabilities in public-facing applications to gain initial access.

Execution:

Command and Scripting Interpreter (T1059): Uses command-line interfaces and scripting languages (e.g., PowerShell, cmd.exe) to execute commands.
PowerShell (T1059.001): Executes PowerShell scripts and commands.
Scheduled Task/Job (T1053): Creates or modifies scheduled tasks to maintain persistence.

Persistence:

Registry Run Keys/Startup Folder (T1547.001): Modifies registry keys or startup folders to ensure persistence.

Privilege Escalation:

Exploit Elevated Privileges (T1068): Exploits vulnerabilities to escalate privileges.

Defense Evasion:

Obfuscated Files or Information (T1027): Uses obfuscation techniques to evade detection.
Fileless Malware (T1056): Operates entirely in memory to avoid file-based detection.

Credential Access:

Credential Dumping (T1003): Uses tools like Mimikatz to extract credentials from memory.

Discovery:

Network Service Scanning (T1046): Scans the network for active services and systems.
System Information Discovery (T1082): Gathers information about the system and network.

Lateral Movement:

Remote Desktop Protocol (T1076): Utilizes RDP to move laterally within the network.
Pass the Hash (T1550.002): Leverages hashed credentials to access other systems.

Collection:

Data from Information Repositories (T1213): Collects data from repositories and databases.

Exfiltration:

Exfiltration Over Command and Control Channel (T1041): Exfiltrates data over the same channel used for C2 communication.

Impact:

Data Manipulation (T1565): Alters or corrupts data to achieve objectives or disrupt operations.

Impact / Significant Attacks

SolarWinds Supply Chain Attack (2020):

Overview: The SolarWinds attack was a massive and sophisticated supply chain attack that affected thousands of organizations globally. Attackers inserted malicious code into SolarWinds’ Orion software updates, which were then distributed to customers.

Cobalt Strike’s Role: Attackers used Cobalt Strike among other tools to move laterally within compromised networks and execute additional payloads. This allowed them to maintain persistence and escalate their access within affected organizations.

Targeted Attacks by APT29 (Cozy Bear):

Overview: APT29, also known as Cozy Bear, is a Russian state-sponsored threat group known for its sophisticated cyber espionage campaigns. They have targeted various high-profile organizations, including government agencies and think tanks.

Cobalt Strike’s Role: APT29 has used Cobalt Strike as part of their toolset to conduct post-exploitation activities, including lateral movement and data exfiltration. The flexibility of Beacon aids in maintaining stealth and control over compromised systems.

DarkSide Ransomware Attacks (2021):

Overview: DarkSide is a ransomware group that gained notoriety for its high-profile attacks, including the Colonial Pipeline attack, which led to significant disruptions in fuel supply.

Cobalt Strike’s Role: DarkSide operators have used Cobalt Strike for initial access and to perform reconnaissance and lateral movement within networks before deploying ransomware. Cobalt Strike’s capabilities facilitate the execution of complex attack chains.

Attacks by FIN7:

Overview: FIN7, also known as Carbanak, is a financially motivated threat group known for targeting financial institutions and retail organizations. They use sophisticated techniques to steal payment card data and conduct financial fraud.

Cobalt Strike’s Role: FIN7 has utilized Cobalt Strike to establish persistence, perform network reconnaissance, and escalate privileges within compromised environments. The tool aids in managing and executing their attack strategies effectively.

Hafnium’s Exploits (2021):

Overview: Hafnium, a state-sponsored group linked to China, exploited vulnerabilities in Microsoft Exchange Server to conduct widespread attacks on organizations globally.

Cobalt Strike’s Role: Following the initial exploitation, Hafnium used Cobalt Strike to carry out post-exploitation activities, including lateral movement and command and control operations within compromised networks.

References

• GrimResource – Microsoft Management Console for initial access and evasion
• Cobalt Strike