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Active vs Passive Reconnaissance in Cyber Security

Cyber Reconnaissance is an advanced form of cyber security intelligence gathering which involves gathering as much information about a target as possible via the use of digital tools and other advanced techniques. It is an important first step in penetration testing and is key to finding many high-priority vulnerabilities. 

By collecting as much data as possible about the target, a tester may find information such as vulnerable software components in use and potentially vulnerable functionality such as hidden debug interfaces listening on an uncommon port. Data collected from reconnaissance can be related to the target’s network and systems, as well as employees and the company itself. 

In addition to identifying and analyzing potential weaknesses, cyber reconnaissance can also be used to identify any malicious activities that may have already taken place. By analyzing the digital infrastructure, organizations can detect any suspicious activity, such as the presence of malware or unauthorized access. This information can then be used to respond to the threat and take the necessary steps to protect the organization from further damage.

Cyber reconnaissance can be divided into two categories: active and passive information gathering. This article will dive deeply into both types including examples of tools that can be used for each one.

What is Passive Reconnaissance?

Passive reconnaissance is a type of network reconnaissance technique used to collect information about a target system or network without directly interacting with the system or network. It does not require any contact or direct interaction with the target system or network, and is usually done by gathering publicly available information such as open source intelligence (OSINT) or by listening to network traffic. This type of reconnaissance is used by attackers to gain information about the target system or network without alerting the target to the attacker’s presence.

This type of recon can often provide a great deal of information about the target system or network. This includes, but is not limited to, IP addresses, domain names, software versions, system configurations, and user accounts. 

Here are some popular tools penetration testers use for passive reconnaissance:

Wireshark: Wireshark is a network protocol analyzer that can be used for passive recon. It can be used to analyze the packets being sent and received by the target system, as well as any other systems connected to the same network. This technique can allow a user to identify open ports and services, operating systems, application versions, and other network data. By analyzing this data, a user can gain valuable information about the target system’s architecture and security.  It can also be used to view traffic from other systems on the same network, including any malicious traffic that is attempting to access the target system.

tcpdump: Tcmpdump is an alternative tool to Wireshark and can also be used for passive recon by capturing network traffic and analyzing the data for information about communications to and from a target system. 

OSINT: OSINT, or Open Source Intelligence, is a collection of publicly available sources of information that can be used in passive recon to collect information on a target. This can include online databases, news outlets, public records, social media posts, and other open sources. 

Netcraft: Netcraft is a web-based tool that can be used in passive recon to gather technical information about a target’s website. It can identify the web server, operating system, IP address, and DNS records, as well as technologies used on the website, such as scripting languages, content management systems, and frameworks. It can also be used to uncover subdomains and services running on the target’s network. This information can be used to map out the target’s infrastructure and help identify potential attack vectors.

Shodan: This tool is widely utilized to find IOT and network devices on the web. It offers data such as potential security weaknesses, Internet Service Provider (ISP), hostnames,  open ports, SSL certificate information, encryption algorithms, and so forth.

Google Hacking (i.e. using search engines): Google Hacking can be used in passive recon to uncover sensitive information that organizations may not have intentionally made public. Testers can use Google search queries to locate sensitive information such as usernames, passwords, emails, web server logs, and other sensitive data that are unintentionally exposed on the web. 

What is Active Reconnaissance?

Active reconnaissance involves actively probing a network with the intent of gathering information about the target. Active reconnaissance is different from passive reconnaissance, which is the practice of gathering information about a target system without directly interacting with it.

Active reconnaissance can be performed in a variety of ways, depending on the tools and methods chosen by the tester. Common active reconnaissance techniques include port scanning, vulnerability scanning, banner grabbing, and social engineering.

Port scanning is a technique used to identify which ports are open on a target system and what services are listening on those ports. This can be used to identify services that may be vulnerable to attack, such as web servers, mail servers, and FTP servers. Service scanning is a technique used to identify what services are running on a particular port. This can be used to identify vulnerable services, such as Telnet.

Vulnerability scanning is a technique used to identify potential vulnerabilities in a target system. This can be used to identify vulnerable software and services, as well as misconfigured systems that may be vulnerable to attack. 

Banner grabbing is a technique used to gather detailed information about a service, such as its version number and the type of encryption it uses. This can be used to identify potential vulnerabilities in the service.

Social engineering is a technique used to obtain information from a target by making use of human interaction. This can be used to gather information such as passwords and other confidential information. It is important to note that social engineering can be used maliciously, so it is important to use it responsibly.

Here are some examples of popular open-source tools penetration testers use for active recon:

Nmap:  Nmap can be used in active reconnaissance to map out the network infrastructure of a target. It can be used to identify open ports, operating systems, and services running on the target. This information can then be used to identify potential vulnerabilities and develop an attack plan. Additionally, Nmap can also be used to fingerprint active hosts, detect firewall rules, and scan for vulnerable services.

OWASP ZAP: OWASP ZAP can be used for active recon by scanning for vulnerabilities in web applications or web services. It can be used to identify potential security issues, such as SQL injection, cross-site scripting, and broken authentication, as well as to test for weak components or configurations. Additionally, OWASP ZAP can be used to simulate malicious attacks, such as brute force or denial of service, to see if the application can withstand them.

Nikito: Nikito is an open source tool used for active reconnaissance. It is used to gather information about a target system by performing various reconnaissance techniques such as port scanning, service scans, OS fingerprinting, and more. It can also be used to gain access to a system by exploiting vulnerabilities. Nikito can be used to uncover information such as open ports, open services, OS type and version, and even exposed vulnerabilities.

What is the difference between active and passive cyber reconnaissance?

Active cyber reconnaissance is when an attacker actively scans a network or system to gain information or to gain access to resources. Passive cyber reconnaissance is when an attacker passively monitors the network or system to identify potential weaknesses or information that can be used to gain access. Passive reconnaissance typically involves monitoring network traffic, analyzing system logs, and searching for open ports or services.


Reconnaissance is a key stage the penetration testing process. Typically, this involves both passive and active information gathering as they both serve different but important roles. Passive information gathering involves using public sources and data gathering without interaction with the target to gain knowledge regarding it while active information gathering requires directly interacting with it. A competent penetration tester should take advantage of both methods to get the most comprehensive results.

Active Vs Passive Reconnaissance In Cyber Security

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