Port Scan

An introduction to Port Scan and Port Protection

Pallavi Vishwakarma
August 1, 2023

Computer ports serve as the main docking point for information moving from software or the Internet to a device or another computer in the network and vice versa. A port scan is a method used to detect open ports on a network or a device. Attackers often use port scanning to identify vulnerabilities that can be exploited to gain unauthorized access to a system. Port scanning can also be used by security professionals to identify potential security weaknesses in a network or system.

Port protection involves implementing security measures to prevent unauthorized access to open ports. This can include configuring firewalls to block access to unused ports, limiting access to open ports to specific IP addresses, and using intrusion detection systems to alert administrators of suspicious activity.

Some of the common ports are

  1. Port (20) UDP: File Transfer Protocol (FTP) used for data transfer.
  2. Port (22) TCP: Secure Shell (SSH) protocol used for FTP, secure logins, and port forwarding.
  3. Port (23) TCP: Telnet protocol for unencrypted communication.
  4. Port (53) UDP: Domain Name System (DNS), which translates internet domain names into machine-readable IP addresses.
  5. Port (80) UDP: World Wide Web HTTP (Hypertext transfer protocol).

Port scanning techniques

Ping scans: Ping scans are internet control message protocol (ICMP) that is used to send a ping request to a computer and wait for a response. It helps to identify whether a network data packet can reach an IP address without any issues. Cybersecurity companies frequently use ping scans to identify gaps in a firewall's coverage and then try to fix them.

XMAS scans: An XMAS scan will send a FIN packet from the server to terminate a connection after a successful transfer of data. If the port is closed, you will receive a response “no more data is available from the sender”. And if no response is received it will indicate that the port is still live and which can be used by the attacker to target these systems. Since FIN packets are rarely observed, it is quite challenging to manually detect them.

Half-open or SYN(short for synchronize) scans: It is a technique used by malicious attackers to determine the status of the port without actually establishing a full connection. In this attacker does not create a connection between the system instead it sends an SYN message, leaving the target hanging which helps them to identify the ports which are currently open on your system.

Methods to Protect the ports

A Port scan is one of the most popular methods used by the attacker to identify vulnerable servers. Your network system will be susceptible to port scans as long as you have a server that is open to the public. However, there are a number of things you may do to reduce your vulnerabilities:

  • A strong Firewall: It prevents unauthorized access to your private network and controls ports and their visibility. Additionally, firewalls have the ability to recognize and stop active port scans.
  • TCP wrappers: TCP wrappers can provide administrators the freedom to allow or restrict access to the servers depending on IP addresses and domain names.
  • Port forwarding: Port forwarding can be used to redirect traffic from one port to another, making it more difficult for attackers to identify open ports.
  • Network segmentation: Segregating networks can help isolate sensitive systems and data, making it more difficult for attackers to gain access to them.
  • Intrusion detection systems: Intrusion detection systems can be used to monitor network traffic and alert administrators of suspicious activity, such as port scanning.
  • Uncover network holes: Businesses can conduct their own internal port scan to identify whether there are more ports open than required. Even they can check their system frequently for any vulnerabilities that might be exploited.

It is important to regularly scan for open ports and implement port protection measures to prevent unauthorized access to sensitive systems and data.

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