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Easy Sniffer

Network tool for A/D CTF

This tool allow you to automatically start tcpdump session on remote host and save capture files (.pcap) on local machine (inspired by remote_sniffer.py)

Thanks to rsync it is possibile to transfer quickly files from remote host to local machine

Dependencies:

  • python3
  • coloredlogs (from pip)
  • tcpdump (on remote host)
  • rsync (both on local machine and remote host)
  • inotify-tools (on local machine)

It's suggested to use Linux or WSL 2.0

Basic config

All configuration must be done in config.json Example:

{
    "connection_info":{
        "vulnbox_ip": "IP_YOUR_VIRTUAL_MACHINE",
        "vulnbox_port" : 22,
        "user" : "root",
        "ssh_key" : "YOUR_SSH_KEY"

    },
    "tcpdump_info": {
        "interface" : "any",
        "remote_pcap_folder" : "",
        "local_pcap_folder" : "",
        "max_packets" : 500,
        "max_size" : 1,
        "packet_name" : "remote_capture",
        "sleep_time" : 15,
        "script_name" : "rename_pcap"
    },
    "verbose": true
}

Connection Info: information regarding remote connection to the vulnerable virtual machine

  • vulnbox_ip: ip address of the vulnerable virtual machine
  • vulnbox_port: ssh port of the vulnerable virtual machine (default = 22)
  • user: username of the virtual machine (default = root)
  • ssh_key: ssh key used to access remote machine with ssh without using the password

tcpdump info: information regarding packet capture generation and transport to local machine

  • interface: network interface on which tcpdump listen for traffic
  • remote_pcap_folder: folder (on the virtual machine) where to save generated pcap
  • local_pcap_folder: folder (on the locale machine) where to save generated pcap
  • max_packets: maximum number of packets that tcpdump generates. After the N-th packet it will override starting from the first one.
  • max_size: maximum size of each packet in MByte.
  • packet_name: prefix name of the generated packets. They will be named like "packet_name000", "packet_name001" and so on.
  • sleep_time: time (in seconds) to wait between one call to rsync and another to download packet captures to the local machine
  • script_name: script executed after the generation of the packet capture from tcpdump. This is needed because tcpdump doesn't automatically add the .pcap extension but Caronte needs it to work properly. If you set packet_name to be "packet_name.pcap" then tcpdump will generate packets named: "packet_name.pcap000", which is not good for Caronte.

Global

  • verbose: set logging level to DEBUG if true or INFO if false

SSH Key Generation

You must first generate a SSH key to be able to execute remote commands with ssh

To do, follow:

    ssh-keygen -f key_name
    ssh-copy-id -i key_name.pub user@vulnbox_ip

ssh-copy-id just copies the public key you generated inside authorized_keys of the vulnbox_ip address machine

Attention

Make sure:

  • rename_pcap is present in same the same folder of remote_pcap_folder (the script automatically upload this file, but double check anyway)
  • tcpdump is up to date on remote host
  • to execute aa-complain /bin/tcpdump on remote host (apt-get install apparmor-utils). This is needed to make -z postcommand of tcpdump run properly (error such as permission denied could be issued and packets are not renamed in packetnameXXX.pcap, but remains packetname.pcapXXX - not good for Caronte)
  • rsync is installed both on local and remote machine

For more information on point (3), look at:

https://ubuntuforums.org/showthread.php?t=1501339

https://answers.launchpad.net/ubuntu/+source/tcpdump/+question/168402

If you want something easier, you could create and run a script auto_rename using inotify on the remote host which rename packets generated by tcpdump when the latter close the file descriptor. Or eventually you could use -G instead of -C and use the "timestamp string template" of tcpdump, like name_%(H)_%(M).pcap

Caronte integration

Thanks to @eciavatta it is pretty easy to integrate Caronte. Just use ./feedCaronte . inside the local pcap folder and keep it running. In order to use it, you need to install inotify-tools on the local machine

TODO

  • Check if tcpdump is already running on remote host
  • Add better timing for rsync to be called
  • Add integration with Caronte and Flower (automatic pcap uploader)
  • Add basic web interface for easy settings management and for basic pcap analyzing (similiar to Flower)
  • Dockerize when finished