zardaxt.py

import dpkt
import socket
from dpkt.tcp import parse_opts
import pcapy
from datetime import timedelta
import sys
import signal
import traceback
import json
from zardaxt_tcp_options import decode_tcp_options
from zardaxt_utils import TH_SYN, TH_ACK, load_config, compute_near_timestamp_tick
from zardaxt_logging import log
from zardaxt_api import run_api

"""
Author: Nikolai Tschacher
GitHub: https://github.com/NikolaiT/zardaxt
Date: March/April 2021
Update: July 2023

Allows to fingerprint an incoming TCP/IP connection by the initial SYN packet.

Several fields such as TCP Options or TCP Window Size
or IP fragment flag depend heavily on the OS type and version.

Some code has been taken from: https://github.com/xnih/satori
However, the codebase of github.com/xnih/satori was quite frankly
a huge mess (randomly failing code segments and capturing the errors, not good).

As of 2023, it is actually a complete rewrite.
"""

# do not modify those variables
interface = None
verbose = False
fingerprints = {}
timestamps = {}
config = None
if len(sys.argv) == 2:
    config = load_config(sys.argv[1])
else:
    config = load_config()


def update_file():
    log('writing fingerprints.json with {} objects...'.format(
        len(fingerprints)), 'zardaxt')
    with open('fingerprints.json', 'w') as fp:
        json.dump(fingerprints, fp, indent=2, sort_keys=False)


def signal_handler(sig, frame):
    update_file()
    sys.exit(0)


signal.signal(signal.SIGINT, signal_handler)  # ctlr + c
signal.signal(signal.SIGTSTP, signal_handler)  # ctlr + z


def process_packet(ts, header_len, cap_len, ip_pkt, ip_version):
    """
    We are only considering TCP segments here.

    It likely makes sense to also make a TCP/IP fingerprint for other
    TCP-like protocols such as QUIC, which builds on top of UDP.
    """
    tcp_pkt = None

    if ip_pkt.p == dpkt.ip.IP_PROTO_TCP:
        tcp_pkt = ip_pkt.data

    # Sometimes I get the following error in production:
    # File "/root/zardaxt/zardaxt.py", line 74, in process_packet
    # is_syn = tcp_pkt.flags & TH_SYN
    # AttributeError: 'bytes' object has no attribute 'flags'

    # Honestly I don't know why, let's use hasattr() to check that tcp_pkt
    # has the flags attribute

    if tcp_pkt and hasattr(tcp_pkt, 'flags'):
        is_syn = tcp_pkt.flags & TH_SYN
        is_ack = tcp_pkt.flags & TH_ACK

        addr_fam = socket.AF_INET
        if ip_version == 6:
            addr_fam = socket.AF_INET6

        src_ip = socket.inet_ntop(addr_fam, ip_pkt.src)
        dst_ip = socket.inet_ntop(addr_fam, ip_pkt.dst)

        # The reason we are looking for a TCP segment that has the SYN flag
        # but not the ACK flag is that we are only interested in packets
        # coming from client to server and not the SYN+ACK from server to client.
        if is_syn and not is_ack:
            log('SYN packet from {} to {}'.format(src_ip, dst_ip), 'zardaxt')
            tcp_options = parse_opts(tcp_pkt.opts)
            [str_opts, timestamp, timestamp_echo_reply, mss,
                window_scaling] = decode_tcp_options(tcp_options)

            ip_len = None
            ip_ttl = None
            if ip_version == 4:
                ip_ttl = ip_pkt.ttl
                ip_len = ip_pkt.len
            elif ip_version == 6:
                ip_len = len(ip_pkt)
                # Hop Limit (8 bits)
                # Replaces the time to live field in IPv4.
                # This value is decremented by one at each forwarding node and the packet is discarded
                # if it becomes 0. However, the destination node should process the packet normally
                # even if received with a hop limit of 0.
                ip_ttl = ip_pkt.hlim

            if not fingerprints.get(src_ip, None):
                fingerprints[src_ip] = []

            fingerprints[src_ip].append({
                'ts': ts,
                'header_len': header_len,
                'cap_len': cap_len,
                'src_ip': src_ip,
                'dst_ip': dst_ip,
                'src_port': tcp_pkt.sport,
                'dst_port': tcp_pkt.dport,
                'ip_hdr_length': ip_pkt.hl if ip_version == 4 else None,
                'ip_version': ip_pkt.v,
                'ip_total_length': ip_len,
                'ip_tos': ip_pkt.tos if ip_version == 4 else None,
                'ip_id': ip_pkt.id if ip_version == 4 else None,
                'ip_ttl': ip_ttl,
                'ip_rf': ip_pkt.rf if ip_version == 4 else None,
                'ip_df': ip_pkt.df if ip_version == 4 else None,
                'ip_mf': ip_pkt.mf if ip_version == 4 else None,
                'ip_off': ip_pkt.off if ip_version == 4 else None,
                'ip_protocol': ip_pkt.p,
                'ip_checksum': ip_pkt.sum if ip_version == 4 else None,
                'ip_plen': ip_pkt.plen if ip_version == 6 else None,
                'ip_nxt': ip_pkt.nxt if ip_version == 6 else None,
                # @TODO: this is likely not what we want (Probably just take tcp_off instead)
                'tcp_header_length': tcp_pkt.__hdr_len__,
                'tcp_off': tcp_pkt.off,
                'tcp_window_size': tcp_pkt.win,
                'tcp_checksum': tcp_pkt.sum,
                'tcp_flags': tcp_pkt.flags,
                'tcp_ack': tcp_pkt.ack,
                'tcp_seq': tcp_pkt.seq,
                'tcp_urp': tcp_pkt.urp,
                'tcp_options': str_opts,
                'tcp_options_ordered': ''.join(
                    [e[0] for e in str_opts.split(',') if e]),
                'tcp_window_scaling': window_scaling,
                'tcp_timestamp': timestamp,
                'tcp_timestamp_echo_reply': timestamp_echo_reply,
                'tcp_mss': mss
            })

            if len(fingerprints) > config.get('clear_dict_after', 5000):
                log('Clearing fingerprints dict', 'zardaxt')
                fingerprints.clear()
                timestamps.clear()

            if config.get('store_fingerprints', False):
                if len(fingerprints) > 0 and len(fingerprints) % config.get('write_after', 1000) == 0:
                    update_file()


def main():
    try:
        log('Listen on interface {}'.format(config['interface']), 'zardaxt')
        # snaplen (maximum number of bytes to capture per packet)
        # 120 bytes are picked, since the maximum TCP header is 60 bytes and the maximum IP header is also 60 bytes
        # The IPv6 header is always present and is a fixed size of 40 bytes.
        max_bytes = 120
        # promiscuous mode (1 for true)
        promiscuous = False
        # https://github.com/the-tcpdump-group/libpcap/issues/572
        # The main purpose of timeouts in packet capture mechanisms is to allow the capture mechanism
        # to buffer up multiple packets, and deliver multiple packets in a single wakeup, rather than one
        # wakeup per packet, reducing the number of wakeups (which aren't free),
        # timeout (in milliseconds)
        read_timeout = 1

        # Read from the network interface in live mode
        preader = pcapy.open_live(
            config['interface'], max_bytes, promiscuous, read_timeout)

        # Filter certain traffic
        preader.setfilter(config.get('pcap_filter', ''))

        while True:
            (header, buf) = preader.next()
            eth = dpkt.ethernet.Ethernet(buf)
            # Ignore everything other than IPv4 or IPv6
            if eth.type == dpkt.ethernet.ETH_TYPE_IP or eth.type == dpkt.ethernet.ETH_TYPE_IP6:
                ip_pkt = eth.data
                header_len = header.getlen()
                cap_len = header.getcaplen()
                ts = header.getts()

                ip_version = 4
                if eth.type == dpkt.ethernet.ETH_TYPE_IP6:
                    ip_version = 6

                process_packet(ts, header_len, cap_len, ip_pkt, ip_version)
    except Exception as err:
        log("main() crashed with error: {} and stack: {}".format(
            err, traceback.format_exc()), 'api', level='ERROR')


if __name__ == '__main__':
    # run the API thread
    run_api(config, fingerprints, timestamps)
    # run pcap loop
    main()