🧠 Task Description

Challenge Name: Firewall1
Platform: pwn.college
Goal: Your host at 10.0.0.1 is receiving traffic on port 31337. Block that traffic.

🔍 Reconnaissance

Inspecting /challenge/run:

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

Key Observations:

  • A ClientHost (10.0.0.2) repeatedly sends TCP messages to our host (10.0.0.1) on port 31337.
  • A watchdog on the server checks if no connections have been received for more than 2 seconds.
  • If the server receives no traffic for 2 seconds, it prints the flag. So our goal is simple: block incoming TCP traffic on port 31337 to trigger the watchdog and get the flag. —

Exploitation: Block the Traffic with iptables

Step 1: Try blocking with iptables

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

Success! The traffic is blocked, and after ~2 seconds:

pwn.college{MIWxO03OpMWCAVRnO2ogfkMxSAg.0FO0AjNxwSM0IzMyEzW}

Flag

pwn.college{MIWxO03OpMWCAVRnO2ogfkMxSAg.0FO0AjNxwSM0IzMyEzW}