Ethical Hacking
Module VII
Sniffers
Module Objective
Overview of Sniffers
Understanding Sniffers from a cracker perspective
Comprehending Active and Passive Sniffing
ARP Spoofing and Redirection
DNS and IP Sniffing and Spoofing
HTTPS Sniffing
Illustration of various tools used in the above context

Sniffers – An Introduction
Sniffers monitor network data.
A sniffer can be a self-contained software program or a hardware device with the appropriate software or firmware programming.
Sniffers usually act as network probes or "snoops" -- examining network traffic but not intercepting or altering it.
Some sniffers work only with TCP/IP packets, but the more sophisticated tools can work with many other protocols and at lower levels such as the Ethernet frame.
Security Concern
Users of computer networks unwittingly disclose sensitive information about themselves through the use of insecure software, and protocols.
Standard implementations of widely adopted protocols such as Windows file sharing (CIFS/SMB), telnet, POP3, HTTP and FTP transmit login passwords in clear text, exposing an extremely large segment of the internet population to sniffing-related attacks.
Tool: Ethereal
Tool: Snort
There are three main modes in which Snort can be configured: sniffer, packet logger, and network intrusion detection system.
Sniffer mode simply reads the packets off of the network and displays them for you in a continuous stream on the console.
Packet logger mode logs the packets to the disk.
Network intrusion detection mode is the most complex and configurable configuration, allowing Snort to analyze network traffic for matches against a user defined rule set
Tool: Windump
WinDump is the porting to the Windows platform of tcpdump, the most used network sniffer/analyzer for UNIX.
Tool: Etherpeek
Passive Sniffing
Active Sniffing
EtherFlood
EtherFlood floods a switched network with Ethernet frames with random hardware addresses.
The effect on some switches is that they start sending all traffic out on all ports so that the attacker is able to sniff all traffic on the network.

dsniff
dsniff is a collection of tools for network auditing and penetration testing.
dsniff, filesnarf, mailsnarf, msgsnarf, urlsnarf, and webspy passively monitor a network for interesting data (passwords, e-mail, files, etc.).
arpspoof, dnsspoof, and macof facilitate the interception of network traffic normally unavailable to an attacker (e.g, due to layer-2 switching).
sshmitm and webmitm implement active monkey-in-the-middle attacks against redirected SSH and HTTPS sessions by exploiting weak bindings in ad-hoc PKI.
ARP Spoofing
Sniffing HTTPS and SSH
SSL connection uses a session key to encrypt all data sent by server and client.
SSH is based on the public key encryption idea.
With SSH a session key is transmitted in an encrypted fashion using a public key stored on the server.
As such, these protocols – SSL and SSH are sound from a security standpoint. The problem however lies in the basis of these protocols – namely trust certificates and public keys.
Man in the Middle Attack
Macof, MailSnarf, URLSnarf, WebSpy
Macof floods the local network with random MAC addresses, causing some switches to fail open in repeating mode, and thereby facilitates sniffing.
Mailsnarf is capable of capturing and outputting SMTP mail traffic that is sniffed on the network.
urlsnarf is a neat tool for monitoring Web traffic.
Webspy allows the user to see all the WebPages visited by the victim.
Ettercap
SMAC
Mac Changer
MAC changer is a Linux utility for setting a specific MAC address for a network interface.
It enables the user to set the MAC address randomly. It allows specifying the MAC of another vendor or setting another MAC of the same vendor.
The user can also set a MAC of the same kind (e.g.: wireless card).
It offers a choice of vendor MAC list (more than 6200 items) to choose from.
Iris
NetIntercept
DNS Sniffing and Spoofing
DNS Spoofing is said to have occurred when a DNS entry points to another IP instead of the legitimate IP address.
When an attacker wants to poison a DNS cache, he will use a faulty DNS – which can be his own domain running a hacked DNS server. The DNS server is termed as hacked because the IP address records are manipulated to suit the attacker’s needs.
WinDNSSpoof
This tool is a simple DNS ID Spoofer for Windows 9x/2K.
In order to use it you must be able to sniff traffic of the computer being attacked.
Usage : wds -h

Example : wds -n www.microsoft.com -i 216.239.39.101 -g 00-00-39-5c-45-3b
Summary
A sniffer is a piece of software that captures the traffic flowing into and out of a computer attached to a network.
A sniffer attack is commonly used to grab logins and passwords that are traveling around on the network.
Sniffing can be active or passive.
Popular attack methods include man in the middle attack and session hijacking
On switched networks, MAC flooding and ARP spoofing is carried out.