What is OS Fingerprinting?


How OS Fingerprinting  Works: Fundamentals You Need to Know

Malicious actors use OS fingerprinting techniques to exploit enterprise computer systems for theft, malware, data misuse, and ransomware practices. This article shares insight into OS fingerprinting, how it works, and its risks to help you better understand and mitigate this cyber threat.

With Cybersecurity Ventures estimating 2022 to experience nearly 6 billion Internet users, there is going to be a corresponding rise in cyber threats. Moreover, with the growing number of threat actors who can maliciously use computer systems to cause all kinds of harm, organizations and individuals alike need to prepare themselves and safeguard their information assets against threats such as OS fingerprinting. OS fingerprinting could be the entry point for a more significant threat that can have severe implications by exposing the vulnerabilities of the information systems used by organizations. Let's delve deeper into what OS fingerprinting is.

A person holding a computer
Description automatically generated with medium confidence(Image Source: Pixabay)

What is OS Fingerprinting?

The process of analyzing datagrams (data packets) that a computer system distributes across a network to determine the underlying operating system is known as ‘operating system’ or OS Fingerprinting. In simple terms, OS fingerprinting determines a computer's operating system by examining the data it transmits across a network. Both security professionals and hackers use OS Fingerprinting to analyze and map remote networks and determine the security vulnerabilities that might be present and can be exploited.

Types of OS Fingerprinting

There are two types of OS fingerprinting:

  1. Active OS Fingerprinting: Active OS fingerprinting is the technique of identifying the operating system of a target machine by delivering specially designed data packets to the system and studying the TCP/IP (Transmission Control Protocol/Internet Protocols, commonly known as the internet protocol suite) behavior of the system's responses. Active OS fingerprinting is the deliberate transmission of data to a target system for a response to analyze its OS. Generally, Nmap is used by hackers or security professionals for OS detection, by simply typing the following Nmap commands for initiating OS fingerprinting scan, for example:
  2. Passive OS Fingerprinting: Passive OS fingerprinting involves only studying the hidden collection of data packets sent out by a system, i.e., analyzing data packets released on the network by a target system without actively sending it prepared data packets. Cybercriminals choose this approach since it is difficult to detect and can bypass even firewalls. Tools such as p0f can be used to identify remote systems passively. For example, the following command will read fingerprint database from 'filename':

nmap -o target_ip_address


nmap -o target_domain_name

p0f -f filename

or, the following command will list all available interfaces on a network

p0f -L

How Does OS Fingerprinting Work and What Are The Risks?

Threat actors and cybersecurity engineers (usually ethical hackers) utilize OS fingerprinting for different reasons. Cybercriminals exploit machines for malicious purposes, whereas cybersecurity professionals perform OS fingerprinting as part of vulnerability assessment and penetration testing (VAPT) to unearth vulnerabilities to protect the information systems. However, the underlying process of OS fingerprinting remains the same.

One can only implement OS fingerprinting on data packets that have completed a TCP handshake. A TCP handshake is a three-step confirmation between two computer systems for starting a TCP session that ensures SYN for Synchronize, SYN-ACK for Synchronize Acknowledgement, and ACK for Acknowledgement.

There are various parameters of a TCP/IP protocol, including:

  • TTL (Time-to-live)
  • TOS (Type of service)
  • Packet Size
  • Window Size
  • DF Bit (Don't Fragment Bit)

Different OS has different values for these parameters, which threat actors can analyze to determine the vulnerabilities in the system's OS.

After knowing the type of OS a system uses, a threat actor can exploit its vulnerabilities to gain access to the system and its confidential data. Furthermore, gaining access to an administrative system can put an organization's entire network at risk and open doors for data theft, IP theft, financial losses, malware deployment, ransomware, corporate espionage, and more cyber threats.

How to Recognize OS Fingerprinting Threat?

OS Fingerprinting can reveal information about the type of the OS, its version, information about the SNMP (Simple Network Management Protocol), domain names, which malicious actors can leverage to target systems.

Recognition of OS fingerprinting can help assess your organization's cybersecurity posture and help address the vulnerable points. The risk of easier detection accompanies active OS fingerprinting, but passive OS fingerprinting can be challenging to identify as the data being exported is cleverly hidden. If your organization lacks a proper security professional team, it would be best to invest in a vulnerability management solution to assess and monitor your network for OS fingerprinting attacks.

The most popular tools used for OS fingerprinting along with what they provide are:

  • Nmap: The most widely used tool for active OS fingerprinting.
  • Ettercap: A tool for passive OS fingerprinting.
  • P0f: A comprehensive tool for passive OS fingerprinting.

How to Prevent OS Fingerprinting?

The following points highlight what one can do to prevent OS fingerprinting:

  1. Performing Regular Updates: Keeping operating systems updated is one of the most uncomplicated security measures one can adopt. Furthermore, since malicious actors primarily use a browser to export data, keeping the browsers updated can help avoid OS fingerprinting to a reasonable extent.
  2. Deploying Countermeasures: Firewalls and advanced antivirus solutions are valuable tools against OS fingerprinting as they can prevent active OS fingerprinting. In addition, an IDPS (Intrusion Detection and Prevention System) can help protect against OS fingerprinting by monitoring the data packets for identifying potential attacks.
  3. Vulnerability Assessment and Penetration Testing (VAPT): VAPT exercises must be performed regularly. The cadence could be set to a minimum half-yearly or annual. However, VAPT must be conducted if there is a significant change in the enterprise’s IT environment, including operating system, network, etc.
  4. Robust Control & Monitor Policies: Organizations can prevent OS fingerprinting by thoroughly analyzing their network traffic and putting adequate control and monitoring policies in place.
  5. Active Monitoring: Active and regular monitoring of log files and NICs (Network Interface Cards) for unusual indications and patching or all security vulnerabilities can help prevent OS fingerprinting.
  6. Vulnerability Management Solutions: An excellent vulnerability management solution for ensuring safeguards against OS fingerprinting that monitors the organization's network for identifying vulnerabilities and providing solutions can go a long way to help protect your information systems against OS fingerprinting threats.

Final Words

OS fingerprinting can cause considerable harm to your organization by revealing vulnerabilities in your networks through the operating systems. As no operating system is perfect and has specific vulnerabilities that cybercriminals can exploit for malicious purposes, organizations must take effective measures, provided in this article, for protection against OS fingerprinting threats. Furthermore, investing in an effective vulnerability management solution can be the best way to ensure 24x7 protection against today's evolving cyber threats.


1.    OS Fingerprinting. (n.d.). Retrieved March 8, 2022, from website:

2.    Tech. (2020, July 25). OS Fingerprinting. Retrieved March 8, 2022, from ITperfection - Network Security website:

3. (N.d.). Retrieved March 8, 2022, from website:

Written by Kent Weigle

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