🧠 Task Description

Challenge Name: Firewall2
Platform: pwn.college
Goal: Your host at 10.0.0.1 is receiving traffic on port 31337.
Block only the traffic from 10.0.0.3, while continuing to allow traffic from 10.0.0.2.

🔍 Reconnaissance

Inspecting the challenge logic from /challenge/run:

root@ip-10-0-0-1:~# cat /challenge/run

Key Logic:

  • Two client hosts:
    • 10.0.0.2 - should remain allowed
    • 10.0.0.3 - must be blocked
  • The server:
    • Tracks the last connection time from both IPs.
    • If 10.0.0.2 is active (connected within 2 seconds) and 10.0.0.3 is silent (no connection in 2 seconds), it reveals the flag.

So the goal is to block 10.0.0.3, while allowing 10.0.0.2.

Exploitation: Selective Traffic Filtering with iptables

To block only 10.0.0.3 on port 31337, use:

iptables -A INPUT -s 10.0.0.3 -p tcp --dport 31337 -j DROP

pwn.college{c8j4FuuJ_RjQCrfC3hmDM6NtfeZ.0VO0AjNxwSM0IzMyEzW}

Flag

pwn.college{c8j4FuuJ_RjQCrfC3hmDM6NtfeZ.0VO0AjNxwSM0IzMyEzW}