Network scanning is crucial for identifying live systems, open ports, and potential vulnerabilities. This guide will walk you through various scanning methods, tools, and best practices to keep your systems secure.
Check for Live Systems
The first step in network scanning is to identify live systems. A ping scan sends ICMP echo request packets to a target. If the system is alive, it responds with ICMP echo reply packets, providing details like TTL and packet size.
Check for Open Ports
Port scanning helps identify open ports, services running on them, and their versions. Nmap is a powerful tool for this purpose.
Types of Scans
1. Connect Scan
This scan identifies open ports by establishing a full TCP handshake with the target.
Nmap
Command:
nmap -sT -v -p- <TargetIP>
2. Half-open Scan (Stealth Scan)
This scan is stealthier, as it does not complete the TCP handshake. Instead, it resets the connection abruptly.
Nmap Command: nmap -sS -v <TargetIP>
3. XMAS Scan
Also known as inverse TCP scanning, this method sends packets with PSH, URG, and FIN flags. Open ports do not respond, while closed ports send a reset response.
Nmap Command: nmap -sX -v <TargetIP>
4. FIN Scan
This scan sends packets with the FIN flag. Open ports do not respond, while closed ports send a reset response.
Nmap Command: nmap -sF -v <TargetIP>
5. ACK Scan
This method sets the ACK flag in the TCP header. The status of the target's ports is determined based on the window size and TTL value of the reset packets received.
Nmap Command: nmap -sA -v <TargetIP>
6. Null Scan
This scan sends TCP packets with no flags. Open ports do not respond, while closed ports send a reset packet.
Nmap Command: nmap -sN -v -p- <TargetIP>
7. Idle Scan
This technique uses an idle machine on the network to mask the attacker's identity and probe the target ports.
Nmap Command:
nmap -Pn -sI ZombieIP <TargetIP>
Banner Grabbing
Banner grabbing collects information about the operating system, service names, and version numbers of services running on the target system. This information helps identify potential vulnerabilities.
Vulnerability Scanning
Automated tools like Nessus and Acunetix scan the target for vulnerabilities such as outdated operating systems, default passwords, plain text protocols, and vulnerable services. This helps identify weak points that attackers could exploit.
Draw Network Diagrams
Using the information gathered, attackers can create network diagrams that reveal the architecture of the target organization. Tools like Network View and OpManager can help in creating these diagrams.
Prepare Proxies
Proxies mask the attacker's IP address and capture information passing through them. Tools like TOR browsers, Onion sites, Proxify, and Psiphon can help maintain anonymity.
Countermeasures
To protect your network from scans and potential attacks, follow these steps:
- Configure IDS and Firewalls: Block probes and unauthorized access.
- Keep Software Updated: Ensure firewalls, routers, and IDS firmware are up-to-date.
- Run Regular Scans: Use port scanners to verify the security of your network.
- Restrict Access: Add firewall rules to limit access to critical ports.
- Disable ICMP Scanning: Prevent ping-based scans by disabling ICMP at the firewall.
Additional Content
Relevant Statistics
According to a report by Positive Technologies, 84% of companies experienced cyberattacks, with 85% of network perimeter vulnerabilities being exploitable. Regular network scanning can help mitigate these risks.
Examples
Example of a Half-open Scan: If you want to scan a target
without being detected, you can use a half-open scan. For instance, using the
command nmap -sS -v <TargetIP>, you can identify open ports
while minimizing the risk of detection.
Different Perspectives
From a Defender's View: Regularly scanning your network for vulnerabilities helps identify and patch weak points before attackers can exploit them.
From an Attacker's View: Understanding various scanning techniques allows attackers to find the best approach to breach a system.
Actionable Tips
- Use Strong Passwords: Avoid using default or weak passwords for any system or service.
- Update Regularly: Keep all systems, applications, and firmware up-to-date.
- Monitor Network Traffic: Use IDS and firewalls to detect and block suspicious activities.
Expanded Content
Network Scanning Tools: Apart from Nmap, tools like Masscan, OpenVAS, and Nikto can also be used for network scanning and vulnerability assessment.
Advanced Scanning Techniques: Learn about more sophisticated methods like OS fingerprinting, service version detection, and script scanning to deepen your understanding of network security.