How to Prevent Cross Site Scripting


Cross-site scripting (XSS) refers to a client-side script injection attack. The attacker intends the victim’s web browser to run malicious scripts by injecting malicious code into a seemingly harmless web page or application. The episode begins when the victim accesses the compromised website or application. The website or app spreads malicious code to the user’s browser. Forums, message boards, and websites with comment sections are common entry points for Cross-site Scripting attacks.

If the user input is not sanitized before being used in the output generated, a webpage or web application is vulnerable to cross-site scripting attacks.. The victim’s browser then needs to interpret this input from the user. XSS vulnerabilities exist in CSS, as well as in ActiveX, Flash, and VBScript. Still, JavaScript is where you’ll most frequently see them since the language is so integral to the typical web experience. Here, you may find the answer to the question o what is cross-site scripting.

What is Cross-site Scripting?

Injection attacks like Cross-Site Scripting (XSS) are conducted by inserting malicious scripts into seemingly trustworthy websites. When an attacker exploits a vulnerability in a web application, they can launch cross-site scripting (XSS) attack on another user. Web applications often fail to validate or encrypt user input before using it in the generated output, making them vulnerable to these attacks.

XSS allows an attacker to deliver a malicious script to a user without their knowledge. The end user’s browser does not know that the hand should not be trusted so it will run the script regardless. When a browser executes a script that appears to have come from a legitimate source, the malicious script can access the user’s cookies, session tokens, and other private data associated with the visited site. Even the HTML content of the page can be altered by these scripts. Types of Cross-Site Scripting provides additional information on the various XSS vulnerabilities.

What is Cross-Site Scripting Prevention?

Cross-site scripting is an attack technique whereby malicious code is run within the browser of an unsuspecting user. Since attacks can be launched anywhere within an XSS-vulnerable web app, preventing them is often tricky. This article delves into frequently asked questions about Cross-Site Scripting (XSS) prevention in contemporary web applications. It answers some of the most pressing concerns developers have about this attack.

Read on to learn about cross-site scripting and how to prevent it. But before we get there, let’s take a quick look at the planning and execution of an XSS attack.

The attacker in an XSS attack creates a malicious script that is sent to the user and then executed by the application browser. The typical method of attack is for the attacker to use an input field to send specially crafted HTML/JavaScript code to the targeted website, where the victim’s modern web browser interprets it.

The web app responds with the executed script as part of the original request. As soon as this occurs, the attacker can access anything saved in cookies, local storage, form values, etc., during the current session. The malicious user may also have full administrative privileges on the victim’s computer.

How Cross-site Scripting Works?

The first step in a cross-site scripting attack is to compromise the target’s server, and the second is to exploit the exploit.

An attacker needs to inject malicious code (payload) into a web page a victim views before the victim’s browser will execute the code.

The next step is for the victim to access the compromised website. If the attack is targeted, the attacker may use phishing or social engineering to get the victim to click on a malicious URL.
Step one requires a vulnerable website that incorporates user input directly into its pages. As a result, if an attacker inserts a malicious string, it will be parsed by the victim’s browser as code and used within the page. In other XSS attacks, the attacker uses social engineering to get the victim to click on a link containing the malicious payload.


How to Prevent Cross-Site Scripting?

It would be best if you sanitized your input to prevent XSS attacks. Input data should never be sent to the browser without first being inspected for malicious code by your application.

Guidelines for Preventing Cross-Site Scripting (XSS)

Avoiding a Cross-Site Scripting (XSS) attack is a challenging task. To prevent various types of XSS vulnerabilities, specific methods must be implemented based on how user input is utilized in a particular context and the programming framework in use. However, you should adhere to some broad strategic principles to keep your web app secure.

Constant vigilance and training

First, we must train and keep our minds alert.
To stay secure, everyone on your web app should know the dangers of cross-site scripting (XSS) vulnerabilities. Developers, QA personnel, DevOps, and SysAdmins should undergo thorough security training. As a first step, you can send them here.

Don’t put any stock in user feedback

Second, you can’t believe anything the user tells you.
Never trusting user input is essential, as it can introduce an XSS vulnerability in the HTML output. Consistency in handling public feedback and information from authenticated and internal users is necessary.

Make use of escaping and encoding.

Employ escaping and encoding.
HTML escape, JavaScript escape, CSS escape, URL escape, etc., are valid methods for escaping/encoding user input. If you need to run, use a library that already exists; otherwise, write your own.

Clean Up Your HTML

There is no way to escape or encode user input that contains HTML without breaking valid tags. When this occurs, you should employ a tried-and-true HTML parsing and cleaning library. You can use HtmlSanitizer for.NET or SanitizeHelper for Ruby on Rails, but the library you pick will depend on the programming language you’re working in.

Flag as HttpOnly

Confirm that the HttpOnly flag has been set. If you’re concerned about a possible XSS vulnerability, turning cookies into HttpOnly will help. If you do that, cookies won’t be read by any Java scripts running in the browser.

Make use of a Content Security Policy.

It is essential to implement a content security policy. By, implementing a Content Security Policy is another good way to lessen the impact of any XSS flaws (CSP). You can use the Content Security Policy (CSP) header in your HTTP responses to control which dynamic resources can load depending on the request’s origin.

Always be scanning

In this seventh step, scanning is done regularly (with Acunetix).
Developers or third-party libraries, modules, and software could introduce XSS vulnerabilities. It is recommended to regularly utilize a web vulnerability scanner, such as Acunetix, on your web applications. Installing the Acunetix plugin for Jenkins will enable automated scanning of all builds.


In conclusion, implementing preventive measures such as input sanitization, constant vigilance, and security training can significantly reduce the risk of cross-site scripting (XSS) attacks. We need to know many cyber security terms and training we need to take to update our knowledge. Organizations can mitigate XSS’s vulnerabilities by not unthinking user input and employing escaping and encoding techniques. Additionally, implementing a content security policy and setting the HttpOnly flag for cookies adds an extra layer of protection. Regular scanning with a web vulnerability scanner like Acunetix helps identify existing vulnerabilities and ensures ongoing security for web applications. By following these best practices, organizations can enhance their defenses against XSS attacks and maintain user data. To learn more, you can have a look IBM blog post here.