In today's cybersecurity landscape, outdated services and unpatched systems remain a critical attack vector. Recently, I conducted a hands-on Linux penetration testing exercise to simulate a real-world attack scenario, and the results reinforced how chained vulnerabilities can lead to full system compromise.

Step 1: Network Reconnaissance & Service Enumeration

The first step in any penetration test is understanding the attack surface. Using Nmap, I performed:

  • Full port scans
  • Service version detection
  • OS fingerprinting

During this phase, I discovered an exposed legacy service — distccd — vulnerable to unauthenticated remote code execution (RCE). This marked the first critical point in the attack chain.

Tools Used: Nmap, Netcat

Step 2: Initial Access via distccd RCE

With the vulnerable distccd service identified, I executed an RCE exploit to gain initial access. This allowed me to open a low-privileged shell under the service user account, providing the first foothold on the system.

Key Lesson: Unpatched, exposed services can provide attackers full system entry without credentials.

None

Step 3: Post-Exploitation Enumeration

After gaining access, I performed detailed local enumeration to understand the system environment:

  • Users and groups
  • Sudo privileges
  • Linux kernel version
  • Installed tools (gcc, wget, curl)

The system was running an end-of-life Linux kernel (3.2.x), which is highly susceptible to known privilege escalation vulnerabilities.

Tools Used: Bash shell, Linux CLI

Step 4: Privilege Escalation with Dirty COW

The outdated kernel enabled exploitation of Dirty COW (CVE-2016–5195), a kernel-level vulnerability that allows local privilege escalation. Using this exploit:

  • Compiled the exploit on the target system
  • Modified system files to escalate privileges
  • Successfully obtained root access

Outcome: Full administrative control over the Linux server.

Skills Demonstrated: Linux privilege escalation, kernel exploitation, post-exploitation analysis

Step 5: Reporting & Lessons Learned

After completing the attack chain, I compiled a client-ready penetration test report including:

  • Vulnerability assessment
  • Exploitation evidence
  • Risk and impact analysis
  • Remediation recommendations

Key Takeaways:

  • Security failures often result from chained vulnerabilities, not single issues
  • Exposed legacy services + unpatched kernels are a high-risk combination
  • Regular patch management, system hardening, and monitoring are essential

Skills & Tools Applied

  • Penetration Testing
  • Linux Security
  • Remote Code Execution (RCE)
  • Linux Privilege Escalation
  • Vulnerability Assessment & Reporting
  • Metasploit Framework
  • Nmap, Bash, gcc

Conclusion

This penetration testing case study highlights the importance of offensive security practices for Linux systems. Simulating real-world attacks helps uncover vulnerabilities before malicious actors do, while demonstrating the full impact of chained exploits.