Cross-Site Scripting (XSS)

Introduction

• Abbreviation: XSS (not CSS due to conflict with Cascading Style Sheets).
• Nature of Attack: Vulnerability where information can be shared between websites via the browser.
• Prevalence: One of the most common vulnerabilities in web-based applications.
• Mechanism: Exploits the trust a browser has in websites, often leveraging JavaScript.

Types of Cross-Site Scripting Attacks

1. Non-persistent (Reflected) Attack

   • Involves a third-party website allowing scripts in user input.
   • Attacker sends a link with a script to a victim.
   • Victim runs the script unknowingly, sharing private info from a trusted site with the attacker.
   • Example: Attacker exploits a site's search engine input to execute malicious scripts.

2. Persistent (Stored) Attack

   • Attacker posts malicious scripts on platforms like social media.
   • Affects all users who visit the page, executing the script in their browsers.
   • Allows widespread attack as the script is shared across users' networks.

Case Study: Subaru Website Vulnerability

• Discovery: Found by security researcher Aaron Guzman in June 2017.
• Token Vulnerability:
  • Subaru site tokens never expired, allowing indefinite access.
  • Attackers could manipulate vehicle management features and add email access.
• XSS Component: Exploiting Subaru’s website vulnerability allowed attackers to capture user tokens.
• Resolution: Subaru addressed and resolved the vulnerabilities upon notification.

Protection Against XSS

• Avoid Clicking Untrusted Links: Especially in emails and messages. Use a browser to type trusted domain names manually.
• JavaScript Controls: Consider disabling or limiting JavaScript via plugins, though this may restrict web functionality.
• Keep Software Updated: Regularly update browsers and applications to patch vulnerabilities.
• Developer Best Practices: Ensure input fields are sanitized to prevent user-script insertion.

Overall, understanding the mechanism of XSS and recognizing how it can be exploited helps in applying the correct preventive measures both as a user and a developer.