Ethical Hacking - Fingerprinting

Basic Steps

Before attacking a system, it is required that you know what operating system is hosting a website. Once a target OS is known, then it becomes easy to determine which vulnerabilities might be present to exploit the target system.

Below is a simple nmap command which can be used to identify the operating system serving a website and all the opened ports associated with the domain name, i.e., the IP address.

$nmap -O -v howcodex.com

It will show you the following sensitive information about the given domain name or IP address −

Starting Nmap 5.51 ( http://nmap.org ) at 2015-10-04 09:57 CDT 
Initiating Parallel DNS resolution of 1 host. at 09:57 
Completed Parallel DNS resolution of 1 host. at 09:57, 0.00s elapsed 
Initiating SYN Stealth Scan at 09:57
Scanning howcodex.com (66.135.33.172) [1000 ports] 
Discovered open port 22/tcp on 66.135.33.172 
Discovered open port 3306/tcp on 66.135.33.172 
Discovered open port 80/tcp on 66.135.33.172 
Discovered open port 443/tcp on 66.135.33.172 
Completed SYN Stealth Scan at 09:57, 0.04s elapsed (1000 total ports) 
Initiating OS detection (try #1) against howcodex.com (66.135.33.172) 
Retrying OS detection (try #2) against howcodex.com (66.135.33.172) 
Retrying OS detection (try #3) against howcodex.com (66.135.33.172) 
Retrying OS detection (try #4) against howcodex.com (66.135.33.172) 
Retrying OS detection (try #5) against howcodex.com (66.135.33.172) 
Nmap scan report for howcodex.com (66.135.33.172) 
Host is up (0.000038s latency). 
Not shown: 996 closed ports 
PORT     STATE SERVICE 
22/tcp   open  ssh 
80/tcp   open  http 
443/tcp  open  https 
3306/tcp open  mysql  

TCP/IP fingerprint: 
OS:SCAN(V=5.51%D=10/4%OT=22%CT=1%CU=40379%PV=N%DS=0%DC=L%G=Y%TM=56113E6D%P= 
OS:x86_64-redhat-linux-gnu)SEQ(SP=106%GCD=1%ISR=109%TI=Z%CI=Z%II=I%TS=A)OPS 
OS:(O1=MFFD7ST11NW7%O2=MFFD7ST11NW7%O3=MFFD7NNT11NW7%O4=MFFD7ST11NW7%O5=MFF 
OS:D7ST11NW7%O6=MFFD7ST11)WIN(W1=FFCB%W2=FFCB%W3=FFCB%W4=FFCB%W5=FFCB%W6=FF 
OS:CB)ECN(R=Y%DF=Y%T=40%W=FFD7%O=MFFD7NNSNW7%CC=Y%Q=)T1(R=Y%DF=Y%T=40%S=O%A 
OS:=S+%F=AS%RD=0%Q=)T2(R=N)T3(R=N)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%RD=0% 
OS:Q=)T5(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=0%S= 
OS:A%A=Z%F=R%O=%RD=0%Q=)T7(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)U1(R= 
OS:Y%DF=N%T=40%IPL=164%UN=0%RIPL=G%RID=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=N% 
OS:T=40%CD=S)

If you do not have nmap command installed on your Linux system, then you can install it using the following yum command −

$yum install nmap

You can go through nmap command in detail to check and understand the different features associated with a system and secure it against malicious attacks.

Quick Fix

You can hide your main system behind a secure proxy server or a VPN so that your complete identity is safe and ultimately your main system remains safe.

Port Scanning

We have just seen information given by nmap command. This command lists down all the open ports on a given server.

PORT       STATE   SERVICE 
22/tcp     open    ssh 
80/tcp     open    http 
443/tcp    open    https 
3306/tcp   open    mysql

You can also check if a particular port is opened or not using the following command −

$nmap -sT -p 443 howcodex.com

It will produce the following result −

Starting Nmap 5.51 ( http://nmap.org ) at 2015-10-04 10:19 CDT 
Nmap scan report for howcodex.com (66.135.33.172) 
Host is up (0.000067s latency). 
PORT    STATE SERVICE 
443/tcp open  https  

Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds

Once a hacker knows about open ports, then he can plan different attack techniques through the open ports.

Quick Fix

It is always recommended to check and close all the unwanted ports to safeguard the system from malicious attacks.

Ping Sweep

A ping sweep is a network scanning technique that you can use to determine which IP address from a range of IP addresses map to live hosts. Ping Sweep is also known as ICMP sweep.

You can use fping command for ping sweep. This command is a ping-like program which uses the Internet Control Message Protocol (ICMP) echo request to determine if a host is up.

fping is different from ping in that you can specify any number of hosts on the command line, or specify a file containing the lists of hosts to ping. If a host does not respond within a certain time limit and/or retry limit, it will be considered unreachable.

Quick Fix

To disable ping sweeps on a network, you can block ICMP ECHO requests from outside sources. This can be done using the following command which will create a firewall rule in iptable.

$iptables -A OUTPUT -p icmp --icmp-type echo-request -j DROP

DNS Enumeration

Domain Name Server (DNS) is like a map or an address book. In fact, it is like a distributed database which is used to translate an IP address 192.111.1.120 to a name www.example.com and vice versa.

DNS enumeration is the process of locating all the DNS servers and their corresponding records for an organization. The idea is to gather as much interesting details as possible about your target before initiating an attack.

You can use nslookup command available on Linux to get DNS and host-related information. In addition, you can use the following DNSenum script to get detailed information about a domain −

DNSenum.pl

DNSenum script can perform the following important operations −

Get the host's addresses
Get the nameservers
Get the MX record
Perform axfr queries on nameservers
Get extra names and subdomains via Google scraping
Brute force subdomains from file can also perform recursion on subdomain that has NS records
Calculate C class domain network ranges and perform whois queries on them
Perform reverse lookups on netranges

Quick Fix

DNS Enumeration does not have a quick fix and it is really beyond the scope of this tutorial. Preventing DNS Enumeration is a big challenge.

If your DNS is not configured in a secure way, it is possible that lots of sensitive information about the network and organization can go outside and an untrusted Internet user can perform a DNS zone transfer.

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