Exercise 5: Kernel Exploit Development

Objective: Gain a deeper understanding of kernel vulnerabilities and how to exploit them for privilege escalation, and learn effective strategies to prevent such exploits.

Scenario: You are conducting a security assessment on a Linux system. The kernel version is outdated, and you suspect it may be vulnerable to known CVEs (Common Vulnerabilities and Exposures). Your task is to identify a kernel vulnerability, exploit it to escalate privileges, and implement patching strategies to secure the system.

Lab Setup

1. Environment:
   • A Linux system with an outdated kernel version (e.g., via a virtual machine or sandboxed environment).
2. Tools Required:
   • Access to CVE databases (e.g., CVE Details, Exploit-DB).
   • A C compiler (e.g., gcc).
   • A vulnerable kernel exploit script (from a trusted source for testing).

Lab Steps

Step 1: Identify a Kernel Vulnerability

Determine the kernel version on the target system:

uname -r 

Example output:

4.4.0-112-generic

Research CVEs for the specific kernel version:

Visit CVE databases (e.g., https://cve.mitre.org/ or https://www.exploit-db.com/).

Look for privilege escalation vulnerabilities affecting the identified kernel version.

Example CVE: CVE-2017-1000112 (Dirty COW).

Step 2: Prepare the Exploit

Download the exploit code for the identified CVE from a trusted resource:

wget https://www.exploit-db.com/download/40847 -O exploit.c

Review the exploit code to ensure it aligns with the vulnerability and does not contain malicious extras.

Compile the exploit using a C compiler:

gcc exploit.c -o exploit

Step 3: Execute the Exploit

Run the exploit as a non-root user:

./exploit

If successful, you should gain root privileges. Verify by running:

whoami

Expected output: root.

Document the exploitation process, including prerequisites, steps, and results.

Step 4: Mitigation and Prevention

Patch the vulnerable kernel by updating the system:

sudo apt update && sudo apt upgrade -y

Ensure that the kernel version is updated to one that is not affected by the CVE.

Verify the new kernel version:

uname -r

Implement additional security measures:

Enable SELinux or AppArmor for additional kernel protection.

Use tools like grsecurity for enhanced security policies.

Configure automatic updates to apply critical patches promptly.

Solution

Explanation:

• Kernel exploits target vulnerabilities in the kernel to execute arbitrary code with elevated privileges. By compiling and executing the exploit, attackers can bypass user restrictions and gain root access.

Prevention:

1. Regular Updates:
   • Always update the kernel and associated packages to the latest stable versions.
2. Security Hardening:
   • Use security modules like SELinux or AppArmor to restrict unauthorized actions.
   • Implement firewall rules to limit access to kernel-level processes.
3. Exploit Mitigation Tools:
   • Use tools like OSSEC or Tripwire for intrusion detection and prevention.
4. Audit and Monitor:
   • Regularly audit system logs and monitor for signs of exploitation attempts.

Testing and Verification

1. Test the exploit on the system post-update to ensure it no longer works.
2. Verify the kernel version and confirm that it is no longer vulnerable to the identified CVE.
3. Document all findings, including the exploitation process and the mitigation strategies implemented.

Reflection

This exercise demonstrates the risks of running outdated kernels and provides a hands-on approach to exploiting and securing kernel vulnerabilities. By completing this lab, you’ve gained valuable experience in identifying, exploiting, and mitigating kernel vulnerabilities to enhance system security.