Create or Modify System Process – PolicyKit – be4sec

MITRE ATT&CK T1543: Create or Modify System Process – PolicyKit

Understanding PolicyKit Exploitation

The MITRE ATT&CK framework is a comprehensive knowledge base of adversary tactics and techniques based on real-world observations. It’s an invaluable resource for cybersecurity professionals to understand and defend against cyberattacks. One of the techniques detailed within the framework is T1543: Create or Modify System Process. This technique covers how attackers can manipulate system processes to gain persistence, elevate privileges, or evade defenses. A specific and notable example of T1543 in action involves the exploitation of PolicyKit (pkexec). Let’s delve into the specifics.

What is PolicyKit?

PolicyKit (also known as pkexec) is a component of Unix-like operating systems (such as Linux) that provides a structured way for unprivileged processes to execute privileged operations. It acts as an authorization framework, allowing users to perform administrative tasks with proper authentication. Instead of directly using sudo, applications can use PolicyKit to request authorization for specific actions.

Why is PolicyKit a Target?

PolicyKit is a prime target for attackers because successful exploitation can lead to significant privilege escalation. If an attacker can manipulate PolicyKit, they can potentially gain root privileges, giving them complete control over the compromised system.

How Attackers Exploit PolicyKit (T1543)

Attackers leverage vulnerabilities within PolicyKit to execute commands with elevated privileges. One of the most prominent examples of this was the CVE-2021-4034 vulnerability, also known as “PwnKit.”

• PwnKit (CVE-2021-4034): This vulnerability was a memory corruption flaw in pkexec. Attackers could exploit it by crafting specific command-line arguments when invoking pkexec. This would cause pkexec to misinterpret the arguments, leading to the execution of arbitrary code with root privileges. The exploit was relatively easy to execute, making it a popular choice for attackers.
  • Illustrative Example (Conceptual): While providing the exact exploit code is generally avoided here for safety reasons, I can provide a conceptual representation of how the exploit worked. The vulnerability involved how pkexec parsed command-line arguments. By crafting a specific sequence of null pointers and arguments, attackers could cause pkexec to execute arbitrary commands as root.

    This simplified example shows how a crafted NULL pointer could disrupt the expected argument parsing, leading to unintended code execution. The actual PwnKit exploit was more complex but followed this general principle.

MITRE ATT&CK Mapping

The exploitation of PolicyKit, particularly through vulnerabilities like PwnKit, aligns with the following MITRE ATT&CK tactics and techniques:

• TA0004 – Privilege Escalation: This is the primary goal of PolicyKit exploitation. Attackers aim to gain higher-level permissions than they initially have.
• T1543 – Create or Modify System Process: PolicyKit is a system process, and attackers manipulate its behavior to achieve their objectives.

Detection and Mitigation

Detecting and mitigating PolicyKit exploitation is crucial for maintaining system security. Here are some key strategies:

Detection:

• System Logging: Monitor system logs for unusual pkexec activity. Look for unexpected command-line arguments or patterns of execution.
• Endpoint Detection and Response (EDR): EDR solutions can help detect malicious processes and suspicious behavior associated with PolicyKit.
  • EDR Rule Example (Conceptual): An EDR system might have a rule that flags any pkexec process that spawns a shell (e.g., sh, bash) with root privileges, especially if the parent process is unexpected.

    

• Intrusion Detection Systems (IDS): Network-based IDS can potentially detect exploit attempts targeting PolicyKit.
• File Integrity Monitoring (FIM): Monitor the PolicyKit executable and related files for any unauthorized modifications.
  • FIM Example (Conceptual): FIM tools can track changes to critical files like the pkexec binary.

    

Mitigation:

• Patching: The most critical mitigation step is to promptly patch PolicyKit vulnerabilities. Software vendors release security updates to address these flaws, and applying them is essential.
• Principle of Least Privilege: Adhering to the principle of least privilege limits the potential impact of a successful exploit. Users should only have the necessary permissions to perform their tasks.
• Security Awareness Training: Educating users about social engineering and phishing attacks can help prevent attackers from gaining initial access to the system.
• Regular Vulnerability Scanning: Regularly scan systems for vulnerabilities, including those affecting PolicyKit, to identify and address potential weaknesses.

Real-World Implications

The exploitation of PolicyKit vulnerabilities like PwnKit demonstrates the real-world consequences of software flaws. Successful exploitation can lead to:

• Full System Compromise: Attackers gain complete control over the affected system.
• Data Breaches: Sensitive data can be accessed, exfiltrated, or encrypted.
• Malware Deployment: Attackers can install malware, such as ransomware or backdoors, to maintain persistence and further their objectives.
• Denial of Service: Attackers can disrupt critical services and cause system outages.

Conclusion

PolicyKit, while a useful component for managing privileges, can be a dangerous attack vector if not properly secured. Understanding how attackers exploit PolicyKit, particularly through vulnerabilities like PwnKit, is essential for cybersecurity professionals. By implementing robust detection and mitigation strategies, organizations can significantly reduce their risk of falling victim to these types of attacks. Patching vulnerabilities promptly, monitoring system activity, and adhering to security best practices are crucial steps in protecting systems from PolicyKit exploitation.