Port Scan

Port Scanning is a port mapping on the network. It is often executing when reconnaissance.

Nmap

Nmap is still the most commonly used tool when scanning ports of the target system. But in recent years, some other tools, such as masscan or rustscan, are also becoming popular because the tools scan faster than nmap.

It's recommened to do as stealth scan (SYN scan) by adding the option -sS. Also it's prefered to add -T2 flag for being polite.

# -sS: SYN Scan
# -sV: Service/Version detection
# -sC: Default NSE (script)
# -T2: Timing template.
# -p-: Scan all ports
sudo nmap -sSVC -p- <target-ip> -T2
sudo nmap -sSVC -p 1-65535 <target-ip>
# -p 1000-1500: Scan ports from 1000 to 1500
sudo nmap -sSVC -p 1000-1500 <target-ip>

# If port scanning on CTF not real organization, use `--min-rate` for increase scan speed.
# --min-rate: Send packets no slower than <number> per second
sudo nmap -sSVC -p- <target-ip> --min-rate 1000

# -A: All detection
sudo nmap -sS -A <target-ip>

UDP Scan

Sometimes you need the UDP scan.

nmap -sU --top-ports 25 <target-ip>
nmap -sU --top-ports 50 --open <target-ip>

Skip Host Discovery

sudo nmap -sS -Pn <target-ip>

Specified Ports

# -p 22,80,88: Scan only 22, 80, 88 ports
sudo nmap -sSVC -p 22,80,88

# --top-ports: Scan top 100 ports
sudo nmap -sS --top-ports 100 <target-ip>

# -p-1000: Scan first 1000 ports
sudo nmap -sS -p-1000 <target-ip>

Network Ranges

# Wildcard
nmap 10.0.0.*

# CIDR (Classless Inter-Domain Routing)
nmap 10.0.0.1/24

Scan Techniques

# FIN scan
nmap -sF <target-ip>

# Xmas scan
nmap -sX <target-ip>

Firewall Bypass

# Fragmented packets
nmap -f <target-ip>

# Specify MTU (Maximum Transmission Unit)
nmap --mtu 16 <target-ip>
nmap --mtu 24 <target-ip>

# Decoy
nmap -D RND:3 <target-ip>

Nmap Scripting Engine (NSE)

nmap -sC <target-ip>
nmap --script vuln <target-ip>

Using Proxychains

First start Tor service.

sudo service tor start
sudo service tor status

To execute the nmap with proxychains, add the proxychains command before the nmap command.

sudo proxychains nmap -sS <target-ip>

Port Knocking

Port knocking is a method of establishing a connection to a networked computer that has no open ports.

for i in <port_1> <port_2> <port_3>;do nmap -Pn -p $i --host-timeout 201 --max-retries 0 <target-ip>;done

# or we can use `curl` command for knocking ports.
# -m: max time in seconds
curl <ip>:<port1> -m 1
curl <ip>:<port2> -m 1
curl <ip>:<port3> -m 1

After that, check if ports opened.

nmap <target-ip>

Massscan

Masscan is a TCP port scanner. It is faster than nmap.

masscan <target-ip>/16
masscan <target-ip>/24

# -p: Ports
masscan <target-ip>/16 -p 80,443
masscan <target-ip>/16 -p 22-80
masscan <target-ip>/16 -p 0-65535
# --top-ports
masscan <target-ip>/16 --top-ports 100

RustScan

RustScan is the modern port scanner. It is faster than nmap.

# -a: Addresses
# --ulimit: Limit system resource amounts
rustscan -a <target-ip-1>,<target-ip-2> --ulimit 5000
rustscan -a 'hosts.txt' --ulimit 5000

# CIDR
rustscan -a 192.168.0.0/30

# -p: Ports
rustscan -a <target-ip> -p 22,80

# Using Docker image (recommended way by the RustScan official)
# -u 0: Run as root
# -it: Interactive mode
# --rm: Remove the container after finishing to execute
docker run -u 0 -it --rm --name rustscan rustscan/rustscan:2.1.1 -a <target-ip> -- -sSVC

We can also use the Nmap arguments as below.

rustscan -a <target-ip> -- -sSVC
rustscan -a <target-ip> -- -sS -A

Naabu

# -p -: Scan all ports
naabu -p - -host <target-ip>

# -sD: Service discovery *under development [2024-02-11]
# -sV: Service version *under development [2024-02-11]
naabu -sD -s -p 22,80,443 -host <target-ip>

References

• Nmap

• refabr1k