Cross-Site Scripting – A Simplified and Succinct Explanation

Talking about web app security exploitation, everyday attackers are finding new ways to fulfill their nasty motives. This causes businesses to experience repercussions that are difficult to overcome. One such potential attack is cross-site scripting, where attackers target web applications to exploit their security by inserting malicious code.

However, the question is how cross-site scripting attacks occur in web applications. More importantly, how can it be prevented in web applications?

That's precisely what you will uncover in this blog, along with many other important details that will eventually help you intensify your web app security. Let's get cracking, shall we?

What is a Cross-Site scripting attack?

Cross-site scripting is a security vulnerability found in websites where attackers insert malicious code into web pages that other users explore. This code typically runs in the victims' browsers, which enables attackers to steal victims' confidential details, mess up web pages, or make changes to the website on behalf of the user without their consent. XSS typically takes place because of improper handling or sanitization of user input, and it can be classified into various types, including Stored, Reflected, and DOM-based XSS.

How does a Cross-Site Scripting Attack Occur?

A cross-site scripting attack takes place when a website approves user input data without conducting a proper validation and authentication process before it's displayed in public. Let's take an example: if a user is allowed to submit comments or messages that might carry harmful code, then attackers can easily insert malicious scripts into that input.

When other users explore that particular content, the script automatically runs into their browsers, which can access or steal their data and cause serious security problems. This happens if a website does not conduct proper security checks and treats malicious code as safe by including it in the web pages that are publicly displayed.

Common Types and Examples of Cross-site Scripting

Let's discover some of the frequently occurring cross-site scripting attacks along with their respective examples. Check out the details below.

1. Stored XSS

Malicious code is permanently stored on the server (e.g., in a database) and delivered to users who view the affected page.

Example: A hacker submits a comment with a script on a forum. As soon as the users view the comment, the script will automatically run into their browsers.

2. Reflected XSS

Harmful code is sent as a part of a URL and instantly reflected back by the server in the response.

Example: A user clicks on the link that carries a malicious script, and then the website reflects this script in its response. This is executed in the users' browser to steal their private details.

3. DOM-based XSS

Malicious code misuses the document object model (DOM) in the user's browser by altering the web page without sending new data to the server.

Example: A website dynamically updates content according to the URL parameters. If these parameters aren't handled correctly, it increases the chances for hackers to inject a script that modifies the page content or steals data directly from the user's browser.

4. Blind XSS

Here, the attacker injects a script that will not start affecting an administrator or a user immediately. It'll start working as soon as the user interacts with the data.

Example: An attacker posts a message on a contact form that carries a malicious script, which only starts working when the admin views that message in an admin panel.

What is the Impact of Cross-site Scripting Attacks?

Cross-site scripting attacks severely impact website security by stealing confidential details such as login credentials and cookies, changing or defacing web pages, and so on. When malicious scripts start running in users'users' browsers, they can hijack users'users' accounts, imitate them, or redirect them to unsafe websites. Cross-site scripting attacks not only affect users' security but also create an adverse impact on the website's reputation, which can cause organizations to suffer critical consequences.

Best Practices to Prevent Cross-site Scripting Attacks

Since XSS attacks are capable of causing a high level of damage to websites' reputations and users' confidentiality, learning robust security practices is a must to prevent them in the best possible way.

1. Input Validation

Ensure all user inputs are checked in accordance with the expected format and content.

2. Sanitize Data

Sanitize user inputs to neutralize malicious characters or scripts.

3. Escape Output

Properly encode data before displaying it on web pages to avoid it from being misunderstood as executable code.

4. Use Security Tools and Frameworks

Use emerging security frameworks and advanced web app security scanner to ensure robust security.

5. Enforce Content Security Policy

Define which sources of scripts are trusted to prevent unauthorized scripts from executing.

6. Use HTTPOnly and Secure Cookies

Set the HTTPOnly and Secure flags on cookies to avoid them from being accessed by scripts and ensure they are only sent over HTTPS.

Summing Up

Cross-site scripting is capable of causing unbearable damage to businesses. We discovered how it impacts the website and how to prevent it with steadfast practice. Hence, using robust and advanced vulnerability scanning tools is no longer an option; they are a must!