The frag3 preprocessor is a target-based IP defragmentation module for Snort.įrag3 is designed with the following goals:Ħ. The format of the preprocessor directive in the Snort config file is: Preprocessors are loaded and configured using the preprocessor keyword. The packetĬan be modified or analyzed in an out-of-band manner using this mechanism.
Preprocessor code is run before theĭetection engine is called, but after the packet has been decoded. Modular plugins into Snort fairly easily. They allow theįunctionality of Snort to be extended by allowing users and programmers to drop Preprocessors were introduced in version 1.5 of Snort. 6 Open Detector Package (ODP) Installation 3 GTP Control Channel Preprocessor Configuration 16 Examples/Default Configuration from nf 14 Example IP specific FTP Client Configuration 13 Example Default FTP Client Configuration 9 Example IP specific FTP Server Configuration
8 Example Default FTP Server Configuration Configuring Snort Previous: 2.1 Includes Contents It works at the packet level, so for example all the magic TCP does for you may have to be accounted for in your code, depending on what you're trying to accomplish.Next: 2.3 Decoder and Preprocessor Up: 2. This mechanism is way more elegant in a certain regard, but also fairly low-level. You then write a userspace tool that receives those packets, makes whatever modifications you want, and then optionally pushes them back onto the network stack.
Essentially what you do is set up an iptables rule that sends the traffic to the target QUEUE. And simply parrot the traffic from one host to the other, monitoring and/or modifying as you go along, using SNAT if that's necessary for what you're trying to accomplish.Īlternatively, you can do some really cool vooodoo with libnetfilter_queue. Then you make a separate outbound connection to wherever the traffic was originally going. As before, use ARP spoofing to get the traffic to your computer, and possibly DNAT rewriting if necessary so that your application recognizes the traffic if your network configuration doesn't jive with the inbound packets. Use typical socket programming techniques. You write a program that listens for connections outbound from your target. This involves writing a bit of code, but the mechanism is pretty simple. The issue is that the IP layer does not respond to a packet meant for another IP address so although C receives the packet at a lower level, it does not get passed "up" the stack. If IP forwarding is off, A fails to connect with: (UNKNOWN) 5555 (?) : Connection timed out. My goal is to get C to pose as B when A runs the last command. Nc -p 5555 -l # Run same thing on attack machine My netcat commands for testing: nc -p 5555 -l # Run on target B, listen on port 5555 How does C, at a low level, redirect requests meant for B to my own machine?Īll systems involved are using BackTrack. Attacker C (that's me) is in between and currently forwarding packets both ways. To rephrase the question: client A is talking to server B. I am aware of tools like Ettercap and SSLstrip, but how would I manually impersonate the target server? In theory, we should be able to modify traffic as well. This allows us to analyze communications using, for example, Wireshark. We set up IP Forwarding using: echo 1 > /proc/sys/net/ipv4/ip_forward I am doing ARP Spoof experimentation with arpspoof and have successfully set up a man in the middle between two machines.