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 synchronously 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.
Note: The engine operates autonomously with a default policy set optimized for a balance between security and performance. No further configuration is required for standard use cases.

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.

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.

Primary Use Cases

  • Large-scale enterprise applications with a mix of legacy (e.g., jQuery, early Angular) and modern (e.g., React, Vue) frontend code.
  • Content Management Systems (CMS) that allow third-party plugins, which may introduce vulnerable or outdated scripts.
  • Financial and e-commerce platforms where data integrity during form submission is of paramount importance.

Technical Notes

After processing, the original form's native submit() method is invoked. This bypasses any further JavaScript event listeners attached to the form, preventing double-sends and ensuring the data is passed directly to the browser's submission engine, thus preserving the original action and method attributes of the form.

This approach has been benchmarked to introduce a mean processing overhead of less than 2ms, making its performance impact negligible for end-users. The bundle size is 1.8KB (gzipped).