What is Cross-site Scripting and How Can You Fix it

Cross-site Scripting (XSS) is a client-side code injection attack. The attacker attempts to launch malicious scripts in the victim’s web browser by including illicit code in a legitimate website or application. When the user visits the webpage or application that runs the harmful code, the attack begins. 

If a website or web application creates unsanitized user input in the output it generates, it is susceptible to XSS. The victim’s browser must then parse this user input. VBScript, ActiveX, Flash, and even CSS are all vulnerable to XSS attacks. However, they are most prevalent in JavaScript because it underpins so many applications.

A website or web application’s security has been jeopardized if an attacker can use an XSS flaw on a web page to execute arbitrary JavaScript in a user’s browser. Unlike any other security hole, XSS is not the user’s responsibility. If it affects your users, it affects you as well.

Cross-site Scripting can be used to deface a website rather than targeting the user. The attacker may use inserted scripts to modify the content of a website or even send the browser to another web page that includes dangerous code.

How Can an Attacker Use JavaScript for Cross-site Scripting?

XSS flaws are seen to be less hazardous than SQL Injection vulnerabilities. The aftereffects of the capacity to execute JavaScript on a website may not appear to be serious at first. Most web browsers keep JavaScript under tight control. JavaScript has limited permissions on the user’s operating system and files. 

How Does Cross-site Scripting Work?

There are two steps to a cross-scripting (XSS) attack:

1. An attacker must first be able to inject malicious JavaScript code (payload) into a web page that the victim views in order to execute it.
2. After that, the victim must go to a website that includes the harmful code. If the assault is targeted toward specific people, the attacker may use social engineering or phishing to send them a harmful URL.

To be feasible, the vulnerable website must immediately incorporate user input into its pages. The victim’s browser can then be used to include a harmful string that will be treated as source code by the web page. 

How Do Attackers Steal Information Through Cross-site Scripting (XSS)?

Cookies are stolen by hackers using XSS all the time. They may masquerade as the victim by utilizing this method. In several methods, the bad guy may send a cookie to his or her own site.

1. The attacker injects a payload into the website’s database by submitting a dangerous form with harmful JavaScript code.
2. The user makes a request for the web page from the webserver.
3. The web server delivers the attacker’s payload as a part of the HTML body to the victim’s browser.
4. The target’s browser executes the harmful script in the HTML body. In this scenario, the attacker captures the victim’s cookie and transmits it to their own server.
5. The attacker only needs to collect the victim’s cookie when the HTTP request reaches the server now.
6. The hacker may now impersonate the victim using the stolen cookie.

How to Protect Your Server from Cross-site Scripting (XSS) Attacks

Your application must validate all input data, ensure that only the allow listed data is allowed, and guarantee that every variable output in a page is encoded before it is returned to the user to prevent cross-site scripting attacks.

When you encode variable output, you replace HTML syntax with entities, which are alternate representations. The entities are seen in the browser, but they are not run. The entities are transformed back to HTML and printed when they are rendered by a browser, but they are not run.

Now, more than ever, being vigilant online is imperative. Taking efficient cybersecurity measures is paramount to avoid any data breach and loss on your end as a user.