Cross Site Scripting (XSS) | Introduction

Cross Site Scripting (XSS) | Introduction 

Cross Site Scripting allows an attacker to embed malicious JavaScript, VBScript, ActiveX, HTML, or Flash into a vulnerable dynamic page to fool the user, executing the script on his machine in order to gather data. The use of XSS might compromise private information, manipulate or steal cookies, create requests that can be mistaken for those of a valid user, or execute malicious code on the end-user systems. The data is usually formatted as a hyperlink containing malicious content and which is distributed over any possible means on the internet.

As a hacking tool, the attacker can formulate and distribute a custom-crafted CSS URL just by using a browser to test the dynamic website response. The attacker also needs to know some HTML, JavaScript and a dynamic language, to produce a URL which is not too suspicious-looking, in order to attack a XSS vulnerable website.

Any web page which passes parameters to a database can be vulnerable to this hacking technique. Usually these are present in Login forms, Forgot Password forms, etc…

N.B. Often people refer to Cross Site Scripting as CSS or XSS, which is can be confused with Cascading Style Sheets (CSS).

Types of XSS

There are basically three types of XSS flaws: reflected, stored and DOM-based.

• Reflected or Non-persistent
• Stored or Persistent 
• DOM based