Fixing DOM-based Cross-Site Scripting (DOM XSS)

Vulnerability Analysis

DOM-based Cross-Site Scripting occurs purely on the client-side. JavaScript reads data from a user-controlled source (like window.location.hash or document.referrer) and passes it unsafely to a sink (like document.write, element.innerHTML, or eval).

How it is Detected

Identified by analyzing client-side JavaScript code structures for unsafe inputs and source-sink paths.

Remediation Guidelines

Avoid using innerHTML or document.write for user-controlled strings. Use textContent or secure DOM manipulation APIs instead.

Remediation Script (Vanilla JavaScript)

// VULNERABLE: element.innerHTML = location.hash;
// SECURE REMEDIATION: Using textContent
const targetElement = document.getElementById('output');
targetElement.textContent = window.location.hash.substring(1);