@brickhouse-tech/xml2js

Security-Patched Fork — Prototype Pollution Vulnerability Fixed

The original xml2js package is abandoned. Despite 29+ million weekly downloads, it remains unpatched for a critical prototype pollution vulnerability (CVE-2023-0842) that can compromise application security.

@brickhouse-tech/xml2js is a drop-in replacement with the security fix applied, comprehensive regression tests added, and ongoing maintenance.

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🚨 The Problem

Original Package Status

• 29.1M weekly downloads (as of March 2025)
• Last meaningful commit: Years ago
• Maintainer status: Inactive/abandoned
• Critical CVE: CVE-2023-0842 — Prototype pollution via __proto__ and constructor keys in parsed XML
• Risk exposure: Millions of production applications vulnerable to object injection attacks

The Vulnerability

Malicious XML containing __proto__ or constructor element names can pollute JavaScript's Object prototype chain, potentially leading to:

• Remote code execution (RCE) in certain contexts
• Authentication bypass
• Data exfiltration
• Denial of service (DoS)
• Arbitrary property injection across all objects

Example attack vector:

<root>
  <__proto__>
    <isAdmin>true</isAdmin>
  </__proto__>
</root>

When parsed by vulnerable versions, this XML can inject properties into Object.prototype, affecting all objects in the application.

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✅ The Solution

@brickhouse-tech/xml2js is a community-maintained fork that:

1. Fixes CVE-2023-0842 with hardened property assignment using Object.defineProperty()
2. Adds comprehensive regression tests (3 new test cases covering attack vectors)
3. Maintains 100% API compatibility (drop-in replacement)
4. Provides ongoing security maintenance and dependency updates
5. Stays current with Node.js LTS releases

What We Fixed

Before (Vulnerable)

// Direct property assignment - vulnerable to prototype pollution
obj[key] = value;

After (Secure)

function defineProperty(obj, key, value) {
  // Create a clean descriptor to prevent prototype pollution
  const descriptor = Object.create(null);
  descriptor.value = value;
  descriptor.writable = true;
  descriptor.enumerable = true;
  descriptor.configurable = true;
  Object.defineProperty(obj, key, descriptor);
}

This approach:

• Uses Object.create(null) to prevent descriptor pollution
• Employs Object.defineProperty() for controlled property creation
• Blocks __proto__, constructor, and prototype injection vectors

Test Coverage

We added three comprehensive regression tests to verify the fix:

1. __proto__ element pollution test

   const maliciousXML = '<root><__proto__><polluted>POLLUTED</polluted></__proto__></root>';
   // Verifies Object.prototype.polluted remains undefined

2. constructor element pollution test

   const maliciousXML = '<root><constructor><polluted>POLLUTED</polluted></constructor></root>';
   // Verifies constructor pollution is blocked

3. __proto__ attribute pollution test

   const maliciousXML = '<root><__proto__ polluted="POLLUTED"/></root>';
   // Verifies attribute-based pollution vectors are blocked

All tests verify that Object.prototype.polluted and ({}).polluted remain undefined after parsing malicious XML.

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🔄 Migration Guide

One-Line Installation

npm uninstall xml2js
npm install @brickhouse-tech/xml2js

Code Changes Required

None. This is a 100% drop-in replacement with identical API surface.

// Original
const xml2js = require('xml2js');

// Replacement (same code, secure implementation)
const xml2js = require('@brickhouse-tech/xml2js');

For TypeScript Users

// Original
import * as xml2js from 'xml2js';

// Replacement (identical import)
import * as xml2js from '@brickhouse-tech/xml2js';

Verification

After installation, run your test suite. No code changes should be required. If you encounter any compatibility issues, please open an issue.

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📊 Package Details

• Current Version: 1.1.4
• License: MIT (same as original)
• Node.js: >=18.0.0 (ESM support)
• Repository: github.com/brickhouse-tech/node-xml2js
• NPM: @brickhouse-tech/xml2js

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🏢 Enterprise Support

For organizations requiring guaranteed SLA response times, dedicated security advisories, or priority patch delivery:

Enterprise Support Tiers Available

• 🥉 Bronze: 5-day response, email support
• 🥈 Silver: 48-hour response, security advisory access
• 🥇 Gold: 24-hour response, dedicated Slack channel, custom patches

📧 Contact: brickhouse-tech.lemonsqueezy.com

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💚 Support This Work

This fork is maintained by Brickhouse Tech as a community service. If your organization benefits from this security patch, consider sponsoring ongoing maintenance:

GitHub Sponsors

Sponsorship funds:

• Security research and proactive CVE monitoring
• Dependency updates and compatibility testing
• Long-term maintenance and Node.js LTS support
• Community issue triage and documentation

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📚 Documentation

The API documentation remains unchanged from the original xml2js package. For complete usage examples, see:

• Usage Examples
• Parser Options
• Builder Options
• Processing Functions

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Usage

Quick Start

const xml2js = require('@brickhouse-tech/xml2js');
const xml = "<root>Hello xml2js!</root>";

xml2js.parseString(xml, function (err, result) {
    console.dir(result);
});

With Parser Instance

const xml2js = require('@brickhouse-tech/xml2js');
const parser = new xml2js.Parser();

parser.parseString(xml, function (err, result) {
    console.dir(result);
});

Promise-Based

const xml2js = require('@brickhouse-tech/xml2js');
const xml = '<foo>bar</foo>';

xml2js.parseStringPromise(xml)
  .then(result => console.dir(result))
  .catch(err => console.error(err));

Building XML from Objects

const xml2js = require('@brickhouse-tech/xml2js');
const builder = new xml2js.Builder();

const obj = {name: "Super", Surname: "Man", age: 23};
const xml = builder.buildObject(obj);

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Options

Parser Options

Specify options via new Parser({optionName: value}):

• attrkey (default: $) — Prefix for accessing attributes
• charkey (default: _) — Prefix for accessing character content
• explicitCharkey (default: false) — Use charkey even for elements with no attributes
• trim (default: false) — Trim whitespace at start/end of text nodes
• normalizeTags (default: false) — Lowercase all tag names
• normalize (default: false) — Trim whitespace inside text nodes
• explicitRoot (default: true) — Include root node in result
• emptyTag (default: '') — Value for empty nodes (use factory function for objects)
• explicitArray (default: true) — Always use arrays for child nodes
• ignoreAttrs (default: false) — Ignore all attributes
• mergeAttrs (default: false) — Merge attributes as properties of parent
• validator (default: null) — Custom validation function
• xmlns (default: false) — Include namespace information
• explicitChildren (default: false) — Separate property for child elements
• childkey (default: $$) — Prefix for child elements
• preserveChildrenOrder (default: false) — Ordered children array
• charsAsChildren (default: false) — Treat text as children
• includeWhiteChars (default: false) — Include whitespace-only text nodes
• async (default: false) — Use async callbacks
• strict (default: true) — Strict XML parsing (highly recommended)
• attrNameProcessors (default: null) — Attribute name processing functions
• attrValueProcessors (default: null) — Attribute value processing functions
• tagNameProcessors (default: null) — Tag name processing functions
• valueProcessors (default: null) — Element value processing functions

Builder Options

Specify options via new Builder({optionName: value}):

• attrkey (default: $) — Prefix for attributes
• charkey (default: _) — Prefix for character content
• rootName (default: root) — Root element name
• renderOpts — Rendering options for xmlbuilder-js
  • pretty (default: true) — Prettify output
  • indent (default: ' ') — Indentation string
  • newline (default: '\n') — Newline character
• xmldec — XML declaration attributes
  • version (default: '1.0')
  • encoding (default: 'UTF-8')
  • standalone (default: true)
• doctype (default: null) — Optional DTD
• headless (default: false) — Omit XML header
• allowSurrogateChars (default: false) — Allow Unicode surrogate blocks
• cdata (default: false) — Wrap text in CDATA when necessary

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Processing Attribute, Tag Names and Values

You can provide custom processing functions to transform names and values during parsing:

function nameToUpperCase(name) {
    return name.toUpperCase();
}

xml2js.parseString(xml, {
  tagNameProcessors: [nameToUpperCase],
  attrNameProcessors: [nameToUpperCase],
  valueProcessors: [nameToUpperCase],
  attrValueProcessors: [nameToUpperCase]
}, function (err, result) {
  // All names and values transformed to uppercase
});

Built-in Processors

Available in lib/processors.js:

• normalize — Transform to lowercase
• firstCharLowerCase — Lowercase first character only
• stripPrefix — Remove XML namespace prefix (preserves xmlns)
• parseNumbers — Parse numeric strings to numbers
• parseBooleans — Parse boolean strings to booleans

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Running Tests

npm test          # Run test suite
npm run coverage  # Run with coverage report
npm run lint      # Run ESLint

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Contributing

Contributions welcome! Please:

1. Write tests for new features or bug fixes
2. Follow existing code style (ESLint enforced)
3. Update documentation as needed
4. Open an issue before major changes

This project uses:

• ESM (ECMAScript modules)
• Node.js >=18
• Mocha for testing
• ESLint for code quality

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Security

Reporting vulnerabilities: Please email security issues to the maintainers rather than opening public issues. We'll coordinate disclosure and patches.

Security policy: We monitor CVE databases and dependency advisories. Critical patches are released within 48 hours of disclosure.

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License

MIT License — same as the original xml2js package.

Copyright (c) 2010-2024 Marek Kubica and contributors

Security patches and ongoing maintenance by Brickhouse Tech.

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Credits

Original package by Marek Kubica and the xml2js contributors.

Security fork maintained by:

• Brickhouse Tech — github.com/brickhouse-tech
• Lead Maintainer: Nick McCready

Special thanks to the security research community for identifying and documenting CVE-2023-0842.

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FAQ

Why fork instead of contributing upstream?

The original maintainer has not responded to issues or pull requests in years. With 29M+ weekly downloads at risk, the community needed an immediate, maintained solution.

Is this a permanent fork?

We're committed to maintaining this fork as long as the original remains inactive. If upstream development resumes, we'll evaluate reunification.

Will you add new features?

Our primary focus is security and stability. We accept bug fixes and security patches readily. New features are evaluated case-by-case to maintain compatibility.

How do I verify the security fix?

Run the test suite (npm test) and inspect the three CVE-2023-0842 regression tests in test/parser.test.js. The fix implementation is in lib/parser.js (the defineProperty function).

What if I find a security issue?

Email the maintainers immediately (see Security section). Do not open public issues for vulnerabilities.

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Protect your supply chain. Migrate to @brickhouse-tech/xml2js today.