Reconnaissance is a term used by defense forces, and it means obtaining information about the enemy in a way that does not alert them. The same concept is applied by attackers and penetration testers to obtain information related to the target. Information gathering is the main goal of reconnaissance. Any information gathered at this initial stage is considered important. The attacker working with malicious content builds on the information learned during the reconnaissance stage and gradually moves ahead with the exploitation. A small bit of information that appears innocuous may help you in highlighting a severe flaw in the later stages of the test. A valuable skill for a penetration tester is to be able to chain together vulnerabilities that may be low risk by themselves, but that represent a high impact if assembled.

The aim of reconnaissance in a penetration test includes the following tasks:

• Identifying the IP address, domains, subdomains, and related information using Whois records, search engines, and DNS servers.
• Accumulating information about the target website from publicly available resources such as Google, Bing, Yahoo!, and Shodan. Internet Archive (https://archive.org/), a website that acts as a digital archive for all of the web pages on the internet, can reveal some very useful information in the reconnaissance phase. The website has been archiving cached pages since 1996. If the target website was created recently, however, it will take some time for Internet Archive to cache it.
• Identifying people related to the target with the help of social networking sites, such as LinkedIn, Facebook, Flick, Instagram, or Twitter, as well as tools such as Maltego.
• Determining the physical location of the target using a Geo IP database, satellite images from Google Maps, and Bing Maps.
• Manually browsing the web application and creating site maps to understand the flow of the application and spidering using tools such as Burp Suite, HTTP Track, and ZAP Proxy.

In web application penetration testing, reconnaissance may not be so extensive. For example, in a gray box approach, most of the information that can be gathered at this stage is provided by the client; also, the scope may be strictly limited to the target application running in a testing environment. For the sake of completeness, in this book we will take a generalist approach.