Cross Site Scripting (XSS) | The Basics

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In this following post we will have some basic look over Cross Site Scripting. Cross site scripting is also known as XSS and many times people also abbreviate it as CSS (by the way CSS means Cascading Style Sheets). Commonly XSS is web application attack and not web server attack, it occurs in web application which accepts input without validation and sanitization resulting giving an attacker chance to run a malicious script. XSS vulnerability occurs in a web application due to dynamic nature of a web page which is attained by Java Scripts, VB Scripts, ActiveX controls, Flash contents and scripts and sometimes with help of HTML too.

 

All those scripts and programming languages that are responsible for dynamic contents over a web page are also responsible for XSS attacks. An attacker can take advantage of XSS vulnerability and execute a malicious Java script, VB Script, ActiveX controls, Flash and HTML.

Most security professionals think XSS is lame game since it does not provide any help compromising a remote system, but this is not cent percent true. When circumstances are right you can surely own a system using XSS attack. Also level of catastrophic conditions depends upon where a vulnerable application is used and for what purpose. For example a bank’s web application XSS vulnerability can lead to serious online theft or an attacker who wants to execute a malicious script over several computers using social network. So in fact XSS is not all lame game as compared to SQL injection, command injection and directory transversal attacks.

XSS attacks can be classified into following two types,

Reflected Attacks

Stored Attacks

An attack where the inserted code is permanently stored in target server is known as Stored XSS Attack. An attack where the injected code needs special route to victim like email or hyperlink is known as Reflected XSS Attacks. XSS attacks executes codes with help of browser because it supports all scripts and ActiveX controls also no matter the attack type is reflected or stored the result of XSS will not differ.

Though this was just basic in future posts we will cover how some real web application hacking takes place therefore for practice you’ll need vulnerable applications. Following is list of vulnerable web applications for practice,

Damn Vulnerable Web Application (DVWA)

Vicnum

Bodgelt Store

WackoPicko

Jarlsberg

You can practice web application hacking on any of these or all of these but for some reason I suggest you start with Damn Vulnerable Web Application (DVWA). Download it, read how to install and install it. In next post we will see some real way to find and exploit XSS vulnerability. Till then thanks for reading, have a nice time and keep visiting.