Blocking UDP packet
I want to deny a particular malicious UDP packet. I can readily identify this packet from the rest by looking at the data section, where data offset 2 is 0xaa, data is 0xbb, etc. Are there any tools or code samples that can do this?
Basically, instead of seeing the packet in the following tcpdump, I want to block it. I started to write a proxy but realized I would need to keep sessions and that's a nightmare. Is there an easier way to do this? The firewalls I've seen only block based on port, not on data payload.
tcpdump -i eth1 udp[2:1] = 0xaa and udp[5:2] = 0xbbcc
This is what might be called "deep packet inspection". There is FOSS software to do that, but you will have to search for it. Snort and such tools might help.