Post-exploitation and pivoting in Cybersecurity - Time & Space Complexity

Time Complexity: Post-exploitation and pivoting

O(n²)

Understanding Time Complexity

When attackers gain access to one system, they often try to move to others. This process is called pivoting.

We want to understand how the effort to move through multiple systems grows as the number of systems increases.

Scenario Under Consideration

Analyze the time complexity of the following simplified pivoting process.

for each system in network:
    if system is reachable:
        exploit(system)
        gather_credentials(system)
        add system to compromised_list
        for each new_system in network:
            if new_system not in compromised_list:
                try pivot(new_system)
    

This code tries to exploit reachable systems and then pivot to new systems repeatedly.

Identify Repeating Operations

Identify the loops and repeated attempts to move between systems.

• Primary operation: Looping over all systems to exploit and pivot.
• How many times: For each system, it may attempt to pivot to many others, repeating nested loops.

How Execution Grows With Input

As the number of systems (n) grows, the number of pivot attempts grows faster because each compromised system tries to reach others.

Input Size (n)	Approx. Operations
10	About 100 attempts
100	About 10,000 attempts
1000	About 1,000,000 attempts

Pattern observation: The effort grows roughly by the square of the number of systems.

Final Time Complexity

Time Complexity: O(n²)

This means if you double the number of systems, the work to pivot between them roughly quadruples.

Common Mistake

[X] Wrong: "Pivoting effort grows linearly with the number of systems."

[OK] Correct: Because each compromised system tries to reach many others, the attempts multiply, not just add up.

Interview Connect

Understanding how pivoting scales helps you think like an attacker and defender. It shows why networks with many systems need strong segmentation.

Self-Check

"What if pivoting only tries new systems once per compromised system instead of repeatedly? How would the time complexity change?"

Practice

1. What is the main purpose of post-exploitation in cybersecurity?

easy

A. To prevent unauthorized access to a network

B. To install antivirus software

C. To perform actions after gaining access to a system

D. To encrypt data before sending

Solution

1. Step 1: Understand post-exploitation context

   Post-exploitation refers to activities done after an attacker has gained access to a system.

2. Step 2: Identify main goal

   The main goal is to explore, gather information, and maintain control over the compromised system.

3. Final Answer:

   To perform actions after gaining access to a system -> Option C

4. Quick Check:

   Post-exploitation = actions after access [OK]

Hint: Post-exploitation happens after breaking in [OK]

Common Mistakes:

• Confusing post-exploitation with prevention
• Thinking it means installing security tools
• Mixing it with data encryption

2. Which of the following commands is commonly used to create a pivot in a compromised network?

easy

A. ssh -L 8080:target:80 user@compromised

B. netstat -an

C. ping 192.168.1.1

D. tracert google.com

Solution

1. Step 1: Identify pivoting command

   Pivoting often uses SSH tunneling to forward ports from a compromised system to reach other targets.

2. Step 2: Analyze options

   ssh -L 8080:target:80 user@compromised uses SSH local port forwarding, which is a common pivot technique.

3. Final Answer:

   ssh -L 8080:target:80 user@compromised -> Option A

4. Quick Check:

   SSH tunneling = pivoting method [OK]

Hint: Pivoting uses SSH tunnels like ssh -L [OK]

Common Mistakes:

• Choosing ping or tracert which are just network tests
• Confusing netstat with pivoting
• Not recognizing SSH port forwarding syntax

3. After compromising a machine inside a network, which command sequence best demonstrates pivoting to access another internal host on port 3389?

medium

A. ssh -D 3389 user@compromised

B. ssh -L 3389:192.168.10.5:3389 user@compromised

C. ssh -R 3389:192.168.10.5:3389 user@compromised

D. ssh user@192.168.10.5 -p 3389

Solution

1. Step 1: Understand SSH port forwarding types

   Local forwarding (-L) forwards a local port to a remote host:port, enabling pivoting.

2. Step 2: Match command to pivoting goal

   ssh -L 3389:192.168.10.5:3389 user@compromised forwards local port 3389 to internal host 192.168.10.5 port 3389 via compromised machine, enabling access.

3. Final Answer:

   ssh -L 3389:192.168.10.5:3389 user@compromised -> Option B

4. Quick Check:

   Local port forwarding = pivoting access [OK]

Hint: Use ssh -L for local port forwarding pivot [OK]

Common Mistakes:

• Confusing -L (local) with -R (remote) forwarding
• Using -D which is dynamic SOCKS proxy, not direct pivot
• Trying direct ssh to internal host without pivot

4. You tried to pivot using ssh -R 9000:10.0.0.5:80 user@compromised but cannot access the service on port 9000 locally. What is the most likely issue?

medium

A. You need to use -L instead of -R for local access

B. The target IP 10.0.0.5 is unreachable from compromised machine

C. Port 9000 is blocked by firewall on compromised machine

D. The remote port forwarding (-R) does not expose ports on the local machine

Solution

1. Step 1: Understand difference between -L and -R

   -L forwards local port to remote host; -R forwards remote port to local host.

2. Step 2: Identify access goal

   If you want to access the service locally on port 9000, you need local forwarding (-L), not remote (-R).

3. Final Answer:

   You need to use -L instead of -R for local access -> Option A

4. Quick Check:

   Local access requires -L, not -R [OK]

Hint: Use -L for local, -R for remote port forwarding [OK]

Common Mistakes:

• Mixing up -L and -R options
• Assuming remote forwarding exposes local ports
• Ignoring firewall or network reachability

5. During a penetration test, you have compromised a Linux server inside a network. You want to access a Windows machine on the internal network that only allows RDP on port 3389. Which sequence of actions best achieves pivoting to the Windows machine?

hard

A. Install antivirus on Linux server to monitor Windows traffic

B. Run a port scan from your machine directly on Windows IP to find open ports

C. Use remote desktop client to connect directly to Windows IP from your machine

D. Set up SSH local port forwarding from your machine to Windows RDP port via compromised Linux server

Solution

1. Step 1: Recognize network restrictions

   Direct access to Windows machine is blocked; only accessible via compromised Linux server inside network.

2. Step 2: Use SSH local port forwarding

   Set up SSH tunnel from your local machine forwarding a local port to Windows machine's RDP port through Linux server.

3. Step 3: Connect via forwarded port

   Use RDP client to connect to local forwarded port, effectively pivoting through Linux server.

4. Final Answer:

   Set up SSH local port forwarding from your machine to Windows RDP port via compromised Linux server -> Option D

5. Quick Check:

   Pivoting = SSH tunnel + local port forwarding [OK]

Hint: Pivot by tunneling RDP through compromised Linux server [OK]

Common Mistakes:

• Trying direct connection ignoring network restrictions
• Confusing port scanning with pivoting
• Installing unrelated software like antivirus