What is Cross-Site Scripting (XSS) And How to Prevent it?

Cross-site scripting (XSS) is a client-side code injection cyber-attack that exploits web security vulnerabilities. It holds a decade’s old history and is still used as an effective tool to exploit innocent users. Let’s explore its implications.

Cyberattackers inject malicious malware in legitimate websites making them vulnerable, and the actual attack occurs when the users interact and access their compromised websites. 

Websites that usually become vulnerable vehicles for carrying out Cross-Site Scripting are message boards, forums, and sites that accept comments and feedback. Once the victim uses the vulnerable platform, hackers get a chance to infect the victim’s system and gain full control over it. This can lead to session hijacking, data theft, and much more. 

JavaScript is widely used by cybercriminals for carrying out XSS attacks and can be crafted in multiple ways and languages according to the target websites and browser. 

Types of Cross-Site Scripting (XSS) Attacks

Here are the major forms of XSS attacks: 

• Stored XSS: When the website’s database is used to store malicious scripts.
• Reflected XSS: In this, an HTTP request is used to send data to an application in an unsafe manner.
• DOM-Based XSS: In this type of XSS attack, the execution of malicious code gets triggered by the client-side rather than server-side.

A Simple Flow to Explain The Working of XSS Attack

1. The attackers inject malicious Javascript code into the website’s database.
2. The victim tries to access the webpage from the server.
3. The server connects to the victim’s webpage and injects malicious code into it as a part of the HTML body.
4. When the victim’s browser executes the infected code it sends cookies to the hacker’s server.
5. Once the HTTP request is received at attackers servers they can easily extract and access victims’ cookies.
6. These cookies can now be freely used by attackers for impersonation.

What Are the Possible Uses of XSS Attacks?

• It can be used to inject malicious trojans into website browsers.
• It can be used to steal users’ sensitive and confidential information.
• Apart from this attacker can use it to carry out activities that a user can perform and access data that a user has easy access to.

Preventive Measures Against Cross-Site Scripting (XSS) Attacks

Here are few important and useful tips to prevent XSS attack

• Filter inputs on arrival and ensure that you get valid inputs.
• Encode data on output: User controllable data in HTTP response should be properly validated.
• Use the appropriate response header.
• Follow the content security policy to limit the losses.