Hacking May 25, 2023

What is cross-site scripting?

Cross-site scripting is an application security vulnerability that allows…

Cross-site scripting is an application security vulnerability that allows hackers to inject malicious code, ddt, into websites or mobile apps.


Cross-site scripting (XSS) attacks occur when an attacker injects a piece of code as input. The malicious code is interpreted as DOM markup (content that allows the browser to access an HTML page) and is executed in the victim’s browser. By executing the code in the victim’s browser, attackers can gain access to sensitive data and bypass the homologation policy.

Types of XSS attacks:

Stored XSS

Malicious scripts are injected into a vulnerable application and stored on vulnerable pages within the application. When a victim loads an infected page in the application, the malicious script executes a user session context. Below is an example of a persistent XSS from the Elementor Page Builder tool. A hacker injects malicious JavaScript code into a website. Clicking on the image activates the XSS payload.

Reflexive XSS

The attacker tricks the victim into clicking a malicious link in a vulnerable position. In this case, the reflex script is injected into the user’s browser session and executed as a direct reflection of the HTTP response returned by the server. The attacker injects the XSS into the working URL, and the injected material is returned to the victim’s browser where the payload is executed.

DOM-based XSS

DOM-based XSS also contains malicious links that can be injected into the victim’s browser using the same attack vector as repulsive XSS, but DOM-based XSS requires no interaction with the server. The malicious code is stored and executed in the browser. The cybercriminal embeds a malicious script in the URL, and when connected to that page, the victim’s browser parses the HTML page to get to the script, executes it, and extracts the malicious JavaScript. Therefore, server-side code protection does not protect against DOM-based XSS attacks. In addition, the server side is independent, making it difficult to detect an attack.

What an attacker can do in an XSS attack?

By injecting code into the victim’s browser, cyber criminals can:
  • Steal sensitive information from the user (login information, credit card information, other personal data);
  • Hijack the user’s session (if the application allows JavaScript to read HTTP session information);
  • Send/receive data from/to a malicious web server;
  • Accessing webcam, microphone, and user location data via HTML5 APIs and other known browser vulnerabilities;
  • Use of advanced phishing techniques that are difficult for both the average user and the experts to recognize;

For an XSS attack to be successful, attackers need to inject malicious content into the site in order to execute it. Therefore, all variables in the web application must be protected. Ensuring that all variables are scanned subsequently excluded or cleared is known as perfect injection resistance. Variables that do not go through this process are potentially vulnerable. With frameworks, perfect robustness can be achieved when all variables are checked, inferred, or cleared.

However, popular frameworks such as React and Angular also have security vulnerabilities. Output coding and HTML cleanup help close these loopholes.

Using Output Coding

If you want to display data as the user enters it, use the platform’s default output encoding. Most platforms have automatic encoding and escaping integrated.

If you are not using a framework or if you need to fill in the security of the framework, you should use the output encoding library. All Variables used in the user interface must be passed through the output encoding function. A list of output encoding libraries is included in the application.

There are many different output encoding methods because browsers analyze HTML, JS, URLs and CSS differently. Using the wrong method can lead to vulnerabilities or reduce the functionality of your application.

Performing HTML Cleanup

Users may need to create their own HTML. The WYSIWYG editor allows clients to change the style and structure of the content. Coding the output here will prevent XSS attacks, but will break the functionality of the application and styles will not be displayed. HTML cleanup should be used in this case.


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