DOM BASED XSS

WHAT IS DOM BASED XSS?

DOM-Based XSS is a type of Cross-Site Scripting vulnerability where the malicious script is executed in the browser by modifying the Document Object Model (DOM) of the webpage. Unlike Stored XSS or Reflected XSS, the attack payload does not travel to the server; instead, it is processed entirely within the browser.

HOW DOES DOM BASED XSS WORK?

1.Client-Side Attack: DOM XSS exploits vulnerabilities in client-side JavaScript.

2.DOM Manipulation: Malicious scripts alter the webpage's structure (DOM).

3.No Server Round Trip (Initially): The malicious payload isn't first sent to the server.

4.Unsanitized Input: Client-side code uses user input (e.g., from the URL) directly without proper sanitization, creating the vulnerability.

5.Impact: Cookie theft, redirection, defacement, etc., in the victim's browser.

MITIGATION FOR DOM BASED XSS?

1.Filter Input on Arrival – Validate and sanitize user input strictly based on expected data types to block malicious input early.

2.Encode Data on Output – Properly encode output before rendering to prevent execution (HTML, URL, JavaScript, and CSS encoding as needed).

3.Use Secure Response Headers – Set Content-Type and X-Content-Type-Options to enforce correct content interpretation by browsers.

4.Implement Content Security Policy (CSP) – Restrict script execution as a final defense against XSS attacks.

CONCLUSION:

DOM Based XSS is a client-side vulnerability where malicious scripts manipulate the webpage's structure (DOM) through unsanitized user input handled by JavaScript. This allows attackers to execute scripts in a victim's browser, potentially leading to cookie theft, redirection, or website defacement. Prevention requires careful input validation, output encoding, and avoiding dangerous JavaScript functions.