osirium Posted August 9, 2017 Report Posted August 9, 2017 Writing my first shellcode - iptables -P INPUT ACCEPT " I've recently started to look into basic application security concepts using the imho excellent material from OpenSecurityTraining.info. In this blogpost I'd like to share my first piece of shellcode executing iptables -P INPUT ACCEPT. **Background** After practically learning how to exploit a simple stackoverflow I wanted to see if I could write my own shellcode. I somehow came across the shellcode repository at shell-storm.org and wanted to develop something that wasn't already in there and is somehow useful. There are multiple entries which execute iptables -F. However, as far as I know, this only flushes all rules from all tables, but doesn't change the default policies. So it may drop all rules, but if a server's default policy is DROP you'll cut the machine off the internet. Mission failed. My idea was to write a piece of shellcode that would change the default policy of the INPUT chain to ACCEPT, i.e. run iptables -P INPUT ACCEPT. Writing shellcode First of all, I'd like to say that I'm not an 1337 sh3llc0d3 3Xp3rt. I read about some basics and tried to understand other people's shellcode and their tricks. So feedback is very welcome! Simply leave a comment or send me an e-mail. The goal is to run /sbin/iptables -P INPUT ACCEPT. At this point we assume that the exploited application has enough privileges to execute this command. Otherwise you might want to add some setuid(0) code or so. " Source: https://0day.work/writing-my-first-shellcode-iptables-p-input-accept/ 2 Quote
