What is Cross Site Scripting? How to prevent XSS attacks?
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Cross Site Scripting

01/03/2021 by admin with 0 comments

What is Cross Site Scripting (XSS)?

These days its far more important to protect the website online application that carry out number of functions. All the robust functionality is only because of JavaScript programming language. JavaScript grants permission to the website to do some pretty cool stuff, it is also unique – with cross site scripting known as the most significant threats.

What is Cross Site Scripting (XSS)?

It means that when hackers or third party attacks the user with malicious JavaScript is called Cross Site Scripting. During the attack, the invalidated inputs are used to change user’s output. The attackers don’t have aim or target the get into the website or application and take advantages of the ones who falls into the hole. Commonly hackers use the easier way that is email message. Server-side languages cannot be affected by the attack that runs on the web pages inside the user’s browser. Exploitation of the commonly used platforms reflects XSS attacks as dangerous and common.


JavaScript proves to be a good client and does not run on the server so it can be used to make amends with the server for performing background request. This background request are used by the attackers for adding up irrelevant content, spams to the web page without even refreshing it.

How does XSS work?

A person sitting at the computer will have eye-site over the file manager, test editor, spreadsheet and music player icons in the lower right corner. Till now everything seems familiar. The missing part is there are tones of internet browsers tabs open at the same time. These tabs will redirect you to funny videos, headlines, ads for sale of essential goods, online stores and speed payment sites. These sites have one thing in common that is JavaScript. Without JavaScript it won’t be possible for the sites to even exist.

A single click on the advertisement link will redirect you to another page. The redirected page contains an online banking page and silently transfers all your saving from your personal account to the attacker’s account. To prevent this kind attacks the browsers it adopts the same-origin-policy (SOP). The following policy gives the assurance of the scripts executed on the web page have no access to the wrong data. Using a different domain wont help if the scripts are loaded and it won’t be possible for the browser to run it.

There are many possibilities of being attacked when the compulsion is easily available on the public pages. The attackers can insert their code to target audience by adding their own ads, phishing prompts and other corrupted content.

Types of XSS

  • Stored XSS


Stored Cross site-scripting attacks takes place when the data is stored under non encrypted website and the attackers can place malicious code on the website for making it crash and to other visitors. The initial stage is created by the attacker and the rest follows. This is the most commonly and dangerous type of Cross-Site Scripting.


For instance, the security passwords and username you have saved on the server by giving consent to the google to save it for you on the page.


  • Reflected Cross-Site Scripting


It occurs when the stored data is sent from a website to the server. For instance, when the user puts up a query to the server through a search bar but the result can only be seen by the user. The attacker sends vulnerable customs link to user to redirect them to the malicious page. For such attacks they grab several ways to confirm their proof of concept.


<input type=”search” value=”potatoes” />

<input type=”search’ value=”Attacker “/><script>StealCredentials()</script>” />


  • Blind Cross-Site Scripting


Blind XSS attacks take place when the attacker cannot see the attacks result. in this type of attacks the vulnerability depends upon the landing page where only the user has access. This method is time consuming and requires lot of preparation to launch it successfully. If the payload fails the attacker won’t be notified for the following.


Attackers always want their code to right with no congestions, to prevent the code from being wrong they use polyglots. The polyglots are designed to work during different situation, in attribute, as plain text or in a script tag.


For instance, the attack occurs when the user id is vulnerable, but only from an administrative page which is restricted for admin users.


  • DOM (Document Object Model)-Based Cross-Site Scripting


DOM Based XSS attacks occur when the website itself non encrypted to XSS, but the JavaScript is. JavaScript works by pasting interactivity on the website post the page is fully loaded. The web application grants permission to change the web page without having access to the server. The main purpose to this is the vulnerability stays the same.

How to prevent XSS attacks?


  • Whitelist values


Whitelist is the list where the user is restricted to input any data. This exercise help to execute and ensure only safe and known servers are being sent to eh server. The restricted user input only works when the user has an idea about what is going to be delivered.


  • Avoid and prohibit HTML in inputs


As we all know HTML is used for rich content and it has access only to minimal and trusted users. For considering use of different ways to create a content, if you allow styling and formatting on an input. While using HTML, don’t forget the important part of sanitizing the and remove the malicious code by using a robust sanitizer DOM Purify.


  • Sanitize value


Sanitizing the web page prevent the malicious code to vanish and the web page becomes secured for the user to operate.


  • Use a WAF to protect against cross site scripting attacks


By using firewall to protect the web page from being attacked virtually.  It helps the intercept the attacks such as XSS, RCE or SQLi before the malicious request reach you website. It also helps in protecting the large size attacks such as DDOS.

After Hacked Action


  • Locate the loophole
  • Delete the malicious content and backdoors
  • Fill the vulnerability
  • Always update your credential
  • Set up a strong WAF


As we all know XSS is used to infiltrate a web page and also attack other users in several ways, to prevent such events from occurring the company or user should approach the security perspectives. The company or the user should scan the web page for potential malicious code and delete them from the web page for the user to operate the web page easily without facing any problems.


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