More Courses

Footprinting & Scanning

Never run any of these tools and techniques on any machine or network without proper authorization!

Mapping a Network

These techniques work both on local and remote. Every host connected to the Internet or a private network must have a unique IP address.

Example:

Block: 200.200.0.0/16
2^16 hosts = 200.200.0.0 - 200.200.255.255

  • ping command tests whether a machine is alive.

  • Ping works by sending one or more special ICMP packets (echo request - Type 8).

  • If the destination host replies with ICMP echo reply.

  • ICMP is part of the IP protocol.

  • fping is an improved version of the ping utility.

  • When running fping on a LAN you are directly attached to, even if you use the -a option, you will get some warning messages about the offline hosts (ICMP Host Unreachable). Those messages are easily removed by: fping -a g 192.168.82.0 192.168.82.255 2>/dev/null.

fping -a -g IPRANGE

# -a option forces the tool to show only alive hosts
# -g option tells the tool we want to perform a ping sweep instead of standard ping

fping -a -g 10.54.12.0/24
fping -a -g 10.54.12.0 10.54.12.255

Nmap Ping Scan

nmap -sn 200.200.0.0/16
nmap -sn -iL hostilist.txt

HOST DISCOVERY:

  • -sL: List Scan - simply list targets to scan.

  • -sn: Ping Scan - disable port scan.

  • -Pn: Treat all hosts as online -- skip host discovery.

  • -PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports.

  • -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes.

  • -PO[protocol list]: IP Protocol Ping.

OS Fingerprinting

  • Possible to identify OS because of some tiny differences in the network stack implementation of the various OS.

  • Signature of the host behavior.

  • The signature is compared against a database of known OS signatures.

  • Offline OS fingerprinting can be done with p0f but we'll use nmap.

nmap -Pn -O <target(s)>
# -Pn switch to skip the ping scan if you already know that the targets are alive

OS DETECTION:

  • -O: Enable OS detection.

  • --osscan-limit: Limit OS detection to promising targets.

  • --osscan-guess: Guess OS more aggressively.

Port Scanning

Goals

  • Prepare for the vulnerability assessment phase.

  • Perform stealth reconnaissance.

  • Detect firewalls.

  • Port Scanning goes after knowing the active targets on the network.

  • Determine what TCP/UDP ports are opened.

  • Also knowing what services are running, software and version, on an specific port.

  • Port scanners automate probes requests and response analysis.

  • Also let you detect if there's a firewall between you and your target.

  • 3-way handshake: If port is closed ➝ RST + ACK.

TCP Connect Scan

  • Simplest way to perform a port scan.

  • If the scanner receives a RST packet, then the port is closed.

  • If the scanner is able to complete the connection, then the port is open.

  • TCP Connect Scans are recoded in the daemon logs (from the app point of view, the probe looks like a legitimate connection).

TCP SYN Scan

  • Default nmap scan.

  • Stealthy by design

  • Sends a SYN packet and analyzes the response coming from the target machine.

  • If a RST packet is received, then port is closed.

  • if a ACK packet is received, then the port is open (and RST packet is sent to the target to stop the handshake).

  • Cannot be detected by looking at daemons logs.

Nmap Scan Types

-sT # performs a TCP connect scan
-sS # performs a SYN scan
-sV # performs a version detection scan

  • -sV version detection scan mixes a TCP connect scan with some probes, which are used to detect what application is listening on a particular port, which isn't stealthy but useful.

  • During version detection scan, Nmap performs a TCP connect and reads from the banner of the daemon listening on a port.

  • If the daemon does not send a banner, nmap sends some probes to understand what application is, by studying its behavior

NMAP Port Scanning

nmap -sn 192.168.1.0/24 > hosts-up.txt
nmap -sT -p80 192.168.1.0/24              # checks for all webservers in this network range
nmap -sS -sV -p 21 192.168.1.0/24         # checks for service version

Specifying targets

# By DNS name:
nmap <scan_type> target1.domain.com target2.domain.com

# With an IP address list
nmap <scan_type> 192.168.1.45 200.200.14.56 10.10.1.3

# CIDR notation
nmap <scan_type> 192.168.1.0/24 200.200.1.0/16

# By using wildcards
nmap <scan_type> 192.168.1.*
nmap <scan_type> 10.10.*.1
nmap <scan_type> 200.200.*.*

# Specifying ranges
nmap <scan_types> 200.200.6-12.*

# Octets Lists
nmap <scan_types> 10.14.33.1,3,17
nmap <scan_type> 10.14,20.3.1,3,17,233

# Choosing the ports to scan `-p`:
nmap -p 21,22,139,445,443,80 <target>
nmap -p 100-1000 <target>

Discovering Network with Port Scanning

  • You might encounter networks that are protected by firewalls and where pings are blocked.

  • It's not uncommon to come across a server that does not respond to pings but has many TCP/UDP ports open.

  • -Pn: forces the scan on a server.

  • If you would like to find an alive host, you can scan typical ports instead of performing a ping sweep.

  • The four most basic TCP ports (22, 445, 80, 443) can be used as indicators of live hosts in the network.

Spotting a Firewall

  • You might often see that a version was not recognized regardless of the open port.

  • Or even the service type is not recognized.

  • tcpwrapped means that the TCP handshake was completed but the remote host closed the connection without receiving any data.

  • --reason nmap flag will show an explanation of why a port is marked as open or closed.

masscan

  • Another interesting tool that can help you to discover a network via probing TCP ports.

  • Designed to deal with large networks and to scan thousands of IP addresses at once.

  • Like nmap but a lot faster, however is less accurate.

  • Maybe best to use this for host discovery and then conduct a detailed scan with nmap against certain hosts.

masscan -p22,80,443,53 -Pn --rate=800 --banners 192.168.0.0/24
masscan -p22,80,443,53 -Pn --rate=800 --banners 192.168.0.0/24 --echo > masscan.conf

Examples: Scanning and OS Fingerprinting

# Perform a Ping Scan with Fping: Run a ping scan on the entire network with fping.
> fping -a -g 10.142.111.0/24 2> /dev/null

# Run a Ping Scan with Nmap
> nmap -sn -n 10.142.111.*

# Run a SYN Scan: This time run nmap only on the alive hosts.
> nmap -sS 10.142.111.1,6,48,96,99,100,213

# Version Detection Scan: Run the version detection scan and spot services running on non-conventional default ports.
> nmap -sV 10.142.111.1,6,48,96,99,100,213

# OS Fingerprinting
> nmap -O 10.142.111.1,6,48,96,99,100,213
PreviousInformation GatheringNextVulnerability Assessment

Last updated

Was this helpful?