🟢Payloads Overview

Cobalt Strike is a legitimate, commercially available penetration testing and red teaming tool used by security professionals to simulate advanced adversary tactics. However, it is also frequently used by threat actors for malicious purposes.

Cobalt Strike’s primary functionality revolves around the creation and deployment of various payloads that facilitate post-exploitation activities, including lateral movement, privilege escalation, and command-and-control (C2) communications.

This document aims to provide an in-depth explanation of Cobalt Strike payloads, how they work, their types, and their practical use cases in both offensive security and adversary simulations.

What is a Cobalt Strike Payload?

In Cobalt Strike, a "payload" refers to the malicious code or software component delivered to a target system as part of the post-exploitation process.

Payloads typically provide the attacker with control over the compromised system and enable them to perform a variety of tasks, such as:

• Command-and-Control (C2) channel establishment

• Data exfiltration

• Lateral movement

• Privilege escalation

• Harvesting credentials

Payloads in Cobalt Strike can be deployed in various ways, including through web shells, exploits, social engineering, or exploiting software vulnerabilities.

Types of Cobalt Strike Payloads

Cobalt Strike supports multiple types of payloads, each designed for different stages of an attack or specific operational goals. The following are some of the most common types of payloads used:

Beacon Payload

The Beacon is the most common Cobalt Strike payload, functioning as the primary mechanism for maintaining persistent access to compromised systems. Once executed, Beacon establishes a connection back to the attacker's C2 server. It operates with various protocols, including HTTP, HTTPS, DNS, and SMB.

Key Features of Beacon:

• Persistence: Beacon can be configured to maintain long-term access.

• C2 Channels: The Beacon can communicate over several different protocols, including HTTP, DNS, HTTPS, and SMB.

• Malleable C2: The Beacon can be customized to make detection more difficult by altering the communication patterns and traffic characteristics.

• Execute Commands: Attackers can issue commands through the Beacon interface to interact with the victim system.

Staged Payloads

A staged payload consists of multiple parts: a small loader or "stager" and a larger payload. The stager is initially delivered to the target system, and it retrieves the full payload from a remote location.

Types of Staged Payloads:

• Windows (x86/x64)

• Linux (x86/x64)

• macOS

Advantages of Staged Payloads:

• Smaller initial size makes the first stage easier to deliver.

• The full payload is retrieved after the initial contact, making it harder to detect on initial execution.

Stage-less Payloads

Stage-less payloads are complete payloads that do not require a stager. They are larger in size but are delivered in a single step, eliminating the need for subsequent payload retrieval.

Advantages of Stage-less Payloads:

• Increased reliability since the entire payload is delivered in one piece.

• Typically used in environments where network conditions or security mechanisms prevent the use of staged payloads.

Shellcode Payloads

Cobalt Strike can generate shellcode that can be executed directly by the target system. Shellcode payloads are typically injected into processes in memory and can be used to bypass antivirus defenses, as they do not require disk persistence.

Common Types of Shellcode Payloads:

• Windows Meterpreter

• Linux/Unix reverse shells

• MacOS reverse shells

Payload Delivery Methods

Cobalt Strike provides a variety of ways to deliver payloads to target systems, each suited to different environments and attack vectors.

Exploiting Vulnerabilities

Cobalt Strike integrates with public exploits or custom exploits that can be used to deliver payloads. For instance, exploiting a vulnerable web application, service, or software can trigger the payload execution.

Social Engineering

Social engineering techniques, such as phishing emails with malicious attachments or links, can be used to convince the target to execute the Cobalt Strike payload.

Lateral Movement

Once an initial system has been compromised, Cobalt Strike can be used to move laterally within the network, using legitimate administrative credentials or exploiting vulnerabilities to deploy additional payloads on other systems.

Web Shells

Web shells allow an attacker to interact with the compromised web server remotely. After gaining access, Cobalt Strike payloads can be uploaded and executed.

Removable Media

In some cases, removable media (e.g., USB drives) are used to carry Cobalt Strike payloads for physical access to a system.

Malleable C2

One of Cobalt Strike's most powerful features is its ability to customize the C2 communication channels via "Malleable C2." This feature allows an attacker to modify the characteristics of Beacon traffic, making it more difficult for security defenses to detect.

Malleable C2 allows for:

• Customizable HTTP/S Requests: Attackers can modify HTTP headers, request paths, and other parts of the request to mimic legitimate traffic.

• Customizable DNS Requests: DNS queries can be encoded to avoid detection by network security tools that monitor DNS traffic.

• Traffic Encryption/Obfuscation: Encrypted communication can make it harder for network defenders to inspect and identify malicious activity.

Malleable C2 configurations are particularly useful for evading detection by intrusion detection/prevention systems (IDS/IPS), firewalls, and security information and event management (SIEM) systems.

Post-Exploitation Capabilities

Once the payload is deployed, attackers can leverage the full suite of post-exploitation tools in Cobalt Strike. These include:

• Privilege Escalation: Cobalt Strike can attempt to escalate privileges on a compromised system by exploiting vulnerabilities or misconfigurations.

• Credential Dumping: Tools like Mimikatz can be invoked through Beacon to dump credentials from memory.

• Keylogging: Attackers can set up keyloggers to capture user input on the compromised machine.

• Fileless Malware: Cobalt Strike can run malicious code entirely in memory, without touching the disk, to avoid detection by traditional antivirus solutions.

• Command Execution: Cobalt Strike allows the attacker to run arbitrary commands on the target system remotely.

Mitigations and Defenses Against Cobalt Strike Payloads

To defend against Cobalt Strike and its payloads, organizations should employ a multi-layered defense strategy:

• Network Segmentation: Segmentation can limit the spread of attacks across the network.

• Endpoint Detection and Response (EDR): Advanced EDR solutions can detect unusual behavior indicative of Cobalt Strike activity.

• Firewall and IDS/IPS Configuration: Anomaly-based detection systems can identify irregular C2 traffic patterns, especially if Malleable C2 is not used effectively.

• User Education and Phishing Awareness: Training employees to recognize phishing emails can reduce the effectiveness of social engineering techniques.

• Monitoring and Logging: Continuous monitoring of logs and network traffic is essential to detect suspicious activity related to Cobalt Strike.

Conclusion

Cobalt Strike remains one of the most potent tools in the arsenals of penetration testers and malicious actors alike. Its flexibility in payload creation and C2 communications make it a favorite for sophisticated threat actors.

Understanding the various payload types and delivery methods is crucial for defenders to recognize and mitigate attacks that leverage Cobalt Strike.

By adopting comprehensive defensive measures, organizations can detect, block, and respond to Cobalt Strike activity, ultimately reducing the risk of successful exploitation in their environments.