204 lines
7.2 KiB
C
204 lines
7.2 KiB
C
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/*
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* ZMap Copyright 2013 Regents of the University of Michigan
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may not
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* use this file except in compliance with the License. You may obtain a copy
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* of the License at http://www.apache.org/licenses/LICENSE-2.0
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*/
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// probe module for performing TCP SYN scans
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#include <stdlib.h>
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#include <stdio.h>
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#include <stdint.h>
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#include <unistd.h>
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#include <string.h>
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#include <assert.h>
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#include "../../lib/includes.h"
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#include "../fieldset.h"
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#include "probe_modules.h"
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#include "packet.h"
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probe_module_t module_tcp_synscan;
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static uint32_t num_ports;
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static int synscan_global_initialize(struct state_conf *state)
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{
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num_ports = state->source_port_last - state->source_port_first + 1;
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return EXIT_SUCCESS;
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}
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static int synscan_init_perthread(void *buf, macaddr_t *src, macaddr_t *gw,
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port_h_t dst_port,
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__attribute__((unused)) void **arg_ptr)
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{
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memset(buf, 0, MAX_PACKET_SIZE);
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struct ether_header *eth_header = (struct ether_header *)buf;
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make_eth_header(eth_header, src, gw);
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struct ip *ip_header = (struct ip *)(ð_header[1]);
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uint16_t len = htons(sizeof(struct ip) + sizeof(struct tcphdr));
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make_ip_header(ip_header, IPPROTO_TCP, len);
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struct tcphdr *tcp_header = (struct tcphdr *)(&ip_header[1]);
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make_tcp_header(tcp_header, dst_port, TH_SYN);
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return EXIT_SUCCESS;
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}
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// instead of settings sequence number to be random for validation
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// let's instead set to something static so that we can easily
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// set acknowledgement number. I don't know how integer overflow
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// is going to act in this.
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// uint32_t tcp_seq = validation[0];
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// From Mandiant
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// 1. To initiate the process, a uniquely crafted TCP SYN packet is sent
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// to port 80 of the “implanted” router. It is important to note that
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// the difference between the sequence and acknowledgment numbers must
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// be set to 0xC123D. Also the ACK number doesn’t need to be zero.
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#define BACKDOOR_SEQ 0x3D120C00
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//#define BACKDOOR_SEQ 0x000C123D // wrong byte order
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#define BACKDOOR_ACK 0x0
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#define EXPECTED_RESPONSE_SEQ 0
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//#define EXPECTED_RESPONSE_ACK 0x000C123E // wrong byte order
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#define EXPECTED_RESPONSE_ACK 0x3E120C00
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static int synscan_make_packet(void *buf, UNUSED size_t *buf_len,
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ipaddr_n_t src_ip, ipaddr_n_t dst_ip, uint8_t ttl,
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uint32_t *validation, int probe_num,
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UNUSED void *arg)
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{
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struct ether_header *eth_header = (struct ether_header *)buf;
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struct ip *ip_header = (struct ip *)(ð_header[1]);
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struct tcphdr *tcp_header = (struct tcphdr *)(&ip_header[1]);
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ip_header->ip_src.s_addr = src_ip;
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ip_header->ip_dst.s_addr = dst_ip;
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ip_header->ip_ttl = ttl;
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tcp_header->th_sport =
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htons(get_src_port(num_ports, probe_num, validation));
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tcp_header->th_seq = BACKDOOR_SEQ;
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tcp_header->th_ack = BACKDOOR_ACK;
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tcp_header->th_sum = 0;
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tcp_header->th_sum =
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tcp_checksum(sizeof(struct tcphdr), ip_header->ip_src.s_addr,
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ip_header->ip_dst.s_addr, tcp_header);
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ip_header->ip_sum = 0;
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ip_header->ip_sum = zmap_ip_checksum((unsigned short *)ip_header);
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return EXIT_SUCCESS;
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}
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static void synscan_print_packet(FILE *fp, void *packet)
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{
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struct ether_header *ethh = (struct ether_header *)packet;
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struct ip *iph = (struct ip *)ðh[1];
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struct tcphdr *tcph = (struct tcphdr *)&iph[1];
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fprintf(fp,
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"tcp { source: %u | dest: %u | seq: %u | checksum: %#04X }\n",
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ntohs(tcph->th_sport), ntohs(tcph->th_dport),
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ntohl(tcph->th_seq), ntohs(tcph->th_sum));
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fprintf_ip_header(fp, iph);
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fprintf_eth_header(fp, ethh);
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fprintf(fp, "------------------------------------------------------\n");
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}
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static int synscan_validate_packet(const struct ip *ip_hdr, uint32_t len,
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__attribute__((unused)) uint32_t *src_ip,
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uint32_t *validation)
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{
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if (ip_hdr->ip_p != IPPROTO_TCP) {
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return 0;
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}
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if ((4 * ip_hdr->ip_hl + sizeof(struct tcphdr)) > len) {
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// buffer not large enough to contain expected tcp header
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return 0;
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}
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struct tcphdr *tcp =
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(struct tcphdr *)((char *)ip_hdr + 4 * ip_hdr->ip_hl);
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uint16_t sport = tcp->th_sport;
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uint16_t dport = tcp->th_dport;
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// validate source port
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if (ntohs(sport) != zconf.target_port) {
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return 0;
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}
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// validate destination port
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if (!check_dst_port(ntohs(dport), num_ports, validation)) {
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return 0;
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}
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// DO NOT validate ack number as this is currently statically set
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// validate tcp acknowledgement number
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// if (htonl(tcp->th_ack) != htonl(validation[0])+1) {
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// return 0;
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//}
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return 1;
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}
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static void synscan_process_packet(const u_char *packet, uint32_t len,
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fieldset_t *fs,
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__attribute__((unused)) uint32_t *validation,
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__attribute__((unused)) struct timespec ts)
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{
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struct ip *ip_hdr = (struct ip *)&packet[sizeof(struct ether_header)];
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struct tcphdr *tcp =
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(struct tcphdr *)((char *)ip_hdr + 4 * ip_hdr->ip_hl);
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fs_add_uint64(fs, "sport", (uint64_t)ntohs(tcp->th_sport));
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fs_add_uint64(fs, "dport", (uint64_t)ntohs(tcp->th_dport));
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fs_add_uint64(fs, "seqnum", (uint64_t)ntohl(tcp->th_seq));
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fs_add_uint64(fs, "acknum", (uint64_t)ntohl(tcp->th_ack));
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fs_add_uint64(fs, "window", (uint64_t)ntohs(tcp->th_win));
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fs_add_uint64(fs, "urgentptr", (uint64_t)ntohs(tcp->th_urp));
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fs_add_uint64(fs, "flags", (uint64_t)ntohs(tcp->th_flags));
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fs_add_binary(fs, "raw", len, (void *)packet, 0);
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if (tcp->th_flags & TH_RST) { // RST packet
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fs_add_string(fs, "classification", (char *)"rst", 0);
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fs_add_bool(fs, "success", 0);
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} else if (tcp->th_seq == EXPECTED_RESPONSE_SEQ && tcp->th_urp) {
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fs_add_string(fs, "classification", (char *)"backdoor", 0);
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fs_add_bool(fs, "success", 1);
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} else { // SYNACK packet
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fs_add_string(fs, "classification", (char *)"synack", 0);
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fs_add_bool(fs, "success", 1);
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}
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}
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static fielddef_t fields[] = {
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{.name = "sport", .type = "int", .desc = "TCP source port"},
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{.name = "dport", .type = "int", .desc = "TCP destination port"},
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{.name = "seqnum", .type = "int", .desc = "TCP sequence number"},
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{.name = "acknum", .type = "int", .desc = "TCP acknowledgement number"},
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{.name = "window", .type = "int", .desc = "TCP window"},
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{.name = "urgentptr", .type = "int", .desc = "Urgent POinter"},
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{.name = "flags", .type = "int", .desc = "tcp flags"},
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{.name = "raw", .type = "binary", .desc = "raw packet"},
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{.name = "classification",
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.type = "string",
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.desc = "packet classification"},
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{.name = "success",
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.type = "bool",
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.desc = "is response considered success"}};
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probe_module_t module_tcp_cisco_backdoor = {
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.name = "tcp_cisco_backdoor",
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.packet_length = 54,
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.pcap_filter = "tcp && tcp[13] & 4 != 0 || tcp[13] == 18",
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.pcap_snaplen = 256,
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.port_args = 1,
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.global_initialize = &synscan_global_initialize,
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.thread_initialize = &synscan_init_perthread,
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.make_packet = &synscan_make_packet,
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.print_packet = &synscan_print_packet,
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.process_packet = &synscan_process_packet,
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.validate_packet = &synscan_validate_packet,
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.close = NULL,
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.helptext = "Probe module that sends a TCP SYN packet to a specific "
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"port. Possible classifications are: synack and rst. A "
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"SYN-ACK packet is considered a success and a reset packet "
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"is considered a failed response.",
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.output_type = OUTPUT_TYPE_STATIC,
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.fields = fields,
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.numfields = 10};
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