What Is Port Scanning?

The port scanning technique is a popular method through which the status of network ports is determined. This process allows the user to identify an open port in a network actively transmitting data. Port scanning also refers to a network data packet’s progression to numerous ports on the host. This technique is commonly undertaken to evaluate network responses and determine potential vulnerabilities in network services to prevent port scan attacks.

Initially, a port scan involves the identification of various active hosts via network scan, which are mapped to their IP address, also known as host discovery. The purpose of conducting a network and port scan is to determine the nature of IP addresses, hosts, and ports. Once done, the user can identify potential loopholes in servers while also analyzing security levels.

One thing to note is that network scanning, and port scans can unveil any active security protocols. Typically, it includes firewalls that exist between the server and connected devices. Once the network scan is complete, the user can observe a list of active hosts compiled during the process. The user can identify any open ports capable of providing unauthorized access.

IT administrators frequently execute port scans to evaluate a network’s active security measures and potential vulnerabilities. At the same time, cyber attackers may utilize the port scan process to commence port scan attacks.

Let us delve a little deeper and see how cybercriminals use port scanning to compromise networks.

What Are Ports And Port Numbers?

Ports of a computer can be perceived as a docking bay from where the transmission of information from a program or the Internet takes place. This information is transmitted to the device or another computer on the same network.

On the other hand, a port number is used to maintain consistency and assist in programming. It is often paired with an IP address to provide key information to the Internet Service Provider for request fulfillment. Port numbers range from 0 to 65,536, with port numbers from 0 to 1023 commonly used for internet use.

Remember that ports are regulated by the Internet Assigned Numbers Authority (IANA). Organizations such as Apple QuickTime and MSN hold these ports.

Here are some of the most renowned ports and their allotted services:

  • Port 20 (UDP) – is the File Transfer Protocol (FTP) allocated for data transmission.
  • Port 22 (TCP) – is the Secure Shell (SSH) protocol allocated for secure logins, port forwarding, and file transfers.
  • Port 53 (UDP) – holds the Domain Name System (DNS) allocated for translating names to IP addresses.
  • Port 80 (TCP) – is known as the World Wide Web HTTP.

Port numbers ranging from 1024 to 49,151 are acknowledged as registered ports that software corporations use. Whereas those ranging from 49,151 to 65,536 are private ports open to everyone.

What Are The Numerous Protocols Used In A Port Scan?

A port scan uses a wide range of protocols, the most common being the TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). Although the purpose of these protocols is the same, that is, data transmission, they follow unique mechanisms. TCP and UDP are the most prominent ports still used today.

TCP is termed as a trustworthy, two-way link-dependent transfer of data that relies on the terminus’ standing for successful data transmission. Meanwhile, UDP is highly unreliable and connectionless. Any data transmitted through the UDP protocol has no concern for the destination’s status. Therefore, data transfer through UDP is not always guaranteed.

What Are The Different Port Scanning Techniques Used Nowadays?

There are a variety of techniques that the user can deploy for port scanning. Typically, the technique implemented depends on the specific goal that the user would like to achieve. Be mindful that cybercriminals would also deploy a specific port scanning approach depending on their goal or port scan attack.

Here are some of the most common port scanning methods and how they work:

Ping Scan

Ping scans are considered the simplest port scans. They are automated internet control message protocol (ICMP) requests sent to numerous servers to gather responses. IT administrators use this approach to debug or block ping scans by deploying firewalls. As a result, it becomes impossible for cyber attackers to exploit or locate a network through pings.

SYN Scan

SYN scan, also known as the half-open scan, is a port scanning approach that cyber criminals utilize to identify a port’s status without creating a full TCP connection. SYN scanning allows attackers to direct SYN packets to the target network to see if it is protected.

An SYN or half-open scan is fast and devious, thus making it suitable to detect open ports on a computer.

FIN Scan

XMAS and FIN scans have a high success rate for commencing cyberattacks since they are less perceptible by firewalls. During FIN scanning, FIN packets are sent to the network by the client, which often goes unnoticed through firewalls.

In the case of an open port, the sender would receive no response. However, an RST response will be generated if the port is closed. Plus, XMAS scans are near impossible to track via monitoring logs, thus making them ideal for learning about the network’s security protocols.

Vanilla Scan

A vanilla scan is a port scanning approach during which a TCP SYN packet is sent to all ports simultaneously. Upon receiving an acknowledgment of connection, it would respond with an ACK flag. Despite being highly accurate, vanilla scans are easily traceable since they establish a full connection that firewalls can easily log.

FTP Bounce Scan

FTP bounce scan enables the sender to disguise their location by sending the packet via an FTP server. Consequently, it allows the sender to go undetected while looking for open ports and connection requests.

Sweep Scan

This approach involves pinging the same port across multiple computer systems connected to a network. Although it does not provide any information regarding the status of the port, it reveals active systems that can be targeted for cyberattacks.

UDP Scan

UDP scanning is used to locate ports that are open to UDP traffic. It is useful, especially if the sender wishes to identify a DNS server or UDP-based services.

TCP Connect Scan

By establishing a full connection, TCP scanning can detect if the target port is open. However, it cannot distinguish between unfiltered and filtered ports with active service.

Port scans can provide loads of data about a target system. Apart from determining systems that are online and which ports are open, port scanners can also reveal applications connected to such ports. At the same time, they can also identify the host’s operating system, thus making it easier for cybercriminals to exploit security loopholes.

What Are The Different Types Of Port Scan Conclusions That May Occur From Port Scanning?

Port scan results can vary depending on the network status. A port scan can reveal if the ports are open, closed, or filtered.

Open Ports

Open ports are an indication that the target network is open to connections. Typically, an open port would respond with a packet, thus revealing its active status. It also specifies that the service used for the scan is also in use.

Locating an open port is the ultimate goal of a port scan. Cyber attackers would perform port scans to exploit security lapses in the network through these ports. In comparison, IT administrators would make efforts to secure these ports by installing firewalls without affecting user workflows.

Closed Ports

Closed ports reveal that the network or server has received the request. However, there is no available service to respond on that port. Be mindful that these ports are also accessible, and cybercriminals can use them to identify the IP address of the targeted host.

A closed port can potentially change into an open port, thus giving rise to potential cyber threats. Therefore, IT administrators must keep a close eye on them. Ideally, they should disable them via a firewall, thus turning it into a filtered port.

Filtered Ports

These ports do not respond to any request that they may receive. This is a common indication that a firewall filtered the sent packet. Cybercriminals cannot extract key information if the sent packet does not reach its desired location.

How Do Cybercriminals Use Port Scans For Data Breaches?

Port scanning is hands down one of the most popular tactics that cyber attackers deploy to hack a network or server. These individuals would use this technique as an initial scan to identify security loopholes in target networks.

Likewise, a port scan allows cybercriminals to detect a server’s or network’s security protocols. As a result, they can map out which of these networks or servers are vulnerable or protected by a firewall.

Be mindful that hackers and cyber attackers almost always disguise their network location while performing a port scan. They deploy various TCP protocol techniques which ensure that their network address remains concealed.

More often than not, attackers would review target networks or servers to see how they respond. They would send packets to multiple ports and record their response. Because the open, closed, or filtered ports respond differently to requests, they can easily identify potentially-weak entry points.

If the port is open, it is most susceptible to cyberattacks. Cybercriminals can use such ports to extract information that can be useful to launch an attack. It includes the type of operating scheme the host uses and their security level.

Bottom Line

Port scanning is a popular technique to troubleshoot network problems that corporations or individuals on a network might face. However, cybercriminals can misuse this approach to compromise networks or servers to gain access to sensitive information. Therefore, efforts must be made to secure numerous ports using firewalls and other evolving security protocols to keep security risks at bay.

Derik Belair

As President and CEO, Derik leads the vision, strategy and growth of Augmentt. Prior to founding Augmentt, Derik was the Vice President at SolarWinds, leading the digital marketing strategy for SolarWinds’ Cloud division. Derik has been working in the channel for over 20 years, starting his career as a channel sales rep at Corel Corp. and eventually becoming the first employee at N-able Technologies in April of 2000.
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