Cross Site Scripting

Overview of cross site scripting (XSS)

What is XSS

XSS (Cross-Site Scripting) is an attack where malicious scripts are injected into a web page, typically by means of a vulnerable form or input field, that are then executed in a user's browser.

The scripts can then steal personal information and sensitive data such as login credentials, financial information, or session tokens.

XSS attacks can be either stored, where the script is stored on the server, or reflected, where the script is reflected back to the user via a search query or other input.

How are XSS attacks carried out

XSS attacks are usually carried out by exploiting vulnerabilities in web applications that allow an attacker to inject malicious code into a website or web application. Here are some common methods used to perform XSS attacks:

Reflected XSS

In this type of attack, the attacker sends a specially crafted link to the victim, which contains malicious code in the URL. When the victim clicks on the link, the malicious code is executed in the victim's browser.

Stored XSS

In this type of attack, the attacker injects malicious code into a web page or web application, which is then stored on the server. When the victim visits the affected page, the malicious code is executed in their browser.

DOM-based XSS

In this type of attack, the attacker exploits a vulnerability in the client-side code (JavaScript) of a web page, which allows them to inject malicious code into the Document Object Model (DOM). This code is then executed by the victim's browser.

Preventing XSS Attacks

There are several ways to prevent XSS attacks in web applications. Here are some best practices to follow:

Input validation

Validate all input from users and sanitize it to ensure that it only contains the expected characters and format. Use server-side validation techniques such as whitelisting or blacklisting to filter out malicious code.

Output encoding

Encode all user-generated content before displaying it to users to prevent malicious code from being executed in the browser. Use encoding techniques such as HTML encoding or URL encoding.

Content Security Policy (CSP)

Implement a content security policy that restricts the types of content that can be loaded on a web page. This can help prevent attackers from injecting malicious scripts into the page.

HTTP-only cookies

Use HTTP-only cookies to prevent client-side scripts from accessing sensitive cookie information, such as session IDs.

Site Maintenance

Regularly update and patch web applications: Keep web applications up-to-date with the latest security patches and updates to address any known vulnerabilities.