The aforementioned network IDS or IPS systems can do more than just track connections—they can also inspect the packets themselves. Usually, these systems are looking for patterns that would signify an attack. For example, a simple rule looking for packets that contain the string
/bin/sh would catch a lot of packets containing shellcode. Our
/bin/sh string is already slightly obfuscated since it's pushed to the stack in four-byte chunks, but a network IDS could also look for packets that contain the strings
These types of network IDS signatures can be fairly effective at catching script kiddies who are using exploits they downloaded from the Internet. However, they are easily bypassed with custom shellcode that ...