Network Scanning: Advanced Nmap Commands and Scripts
As we move beyond basic Nmap scans, we unlock more powerful capabilities for network reconnaissance and vulnerability assessment. Advanced Nmap commands and scripts provide deeper insights into networks, allowing ethical hackers and penetration testers to fine-tune their scanning techniques. This guide covers advanced Nmap functionalities, including custom scans, NSE (Nmap Scripting Engine), and evasion techniques.
Advanced Nmap Scanning Techniques
1. Scanning with Different Timing Options
Nmap provides different timing templates (-T0 to -T5) to control scan speed and stealth.
nmap -T4 example.com-T0(Paranoid Mode): Very slow, avoids detection.-T4(Aggressive Mode): Faster scans for quick results.
2. Scanning Multiple Targets
To scan multiple hosts at once:
nmap 192.168.1.1,192.168.1.2,192.168.1.3Or scan a range:
nmap 192.168.1.0/243. Performing a UDP Scan
Most scans default to TCP, but UDP services may also be vulnerable.
nmap -sU -p 53,161,162 example.com- Common UDP ports: 53 (DNS), 161 (SNMP), 162 (SNMP Trap)
4. Scanning with Custom Port Ranges
Instead of scanning all ports, specify a range for efficiency:
nmap -p 20-100 example.com5. Aggressive Scan with Service and OS Detection
Combines various scanning techniques:
nmap -A example.com- OS detection (
-O) - Version detection (
-sV) - Script scanning (
-sC) - Traceroute (
--traceroute)
Using Nmap Scripting Engine (NSE)
Nmap includes a powerful scripting engine (NSE) to automate vulnerability detection and information gathering.
1. Listing Available Scripts
ls /usr/share/nmap/scripts2. Scanning with Default Scripts
nmap -sC example.comRuns commonly used scripts, including service detection and security checks.
3. Checking for Known Vulnerabilities
nmap --script vuln example.comDetects security weaknesses such as:
- Heartbleed (
ssl-heartbleed) - MS17-010 (EternalBlue exploit)
4. Performing an Advanced Recon Scan
nmap --script=http-title,whois-ip,ssl-cert example.comhttp-title: Retrieves website titles.whois-ip: Performs WHOIS lookups.ssl-cert: Retrieves SSL certificate details.
5. Brute-Force Login Testing
To test for weak credentials on an SSH server:
nmap --script ssh-brute -p 22 example.comEvading Detection with Nmap
1. Spoofing Source IP Address
Use decoys to avoid detection:
nmap -D RND:10 example.com- Generates 10 random decoy IPs to mask the real scan.
2. Fragmenting Packets to Bypass Firewalls
nmap -f example.com- Splits packets to avoid detection by IDS/IPS.
3. Using NULL, FIN, and Xmas Scans
These scan types evade firewalls by sending unexpected TCP flags:
nmap -sN example.com # NULL scan
nmap -sF example.com # FIN scan
nmap -sX example.com # Xmas scanAutomating Nmap Scans
1. Running a Scheduled Scan
Automate scans with a cron job on Linux:
crontab -eAdd the following line to run a scan every day at midnight:
0 0 * * * nmap -A -oN scan_results.txt example.com2. Exporting Scan Results
Save results for later analysis:
nmap -oN output.txt example.com # Normal format
nmap -oX output.xml example.com # XML formatWhy Advanced Nmap Scanning Matters for Hackers
- Detects Stealthy Vulnerabilities: NSE scripts uncover security issues beyond open ports.
- Enhances Evasion Techniques: Learn to bypass security monitoring.
- Automates Penetration Testing: Scripts and scheduled scans streamline security assessments.
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