CVE-2020-28503: Gulpjs Copy-props Prototype Pollution

CVE-2020-28503 Overview

CVE-2020-28503 is a Prototype Pollution vulnerability affecting the copy-props package before version 2.0.5. This npm package, maintained by gulpjs, is vulnerable to Prototype Pollution through its main functionality, which copies properties between objects. Attackers can exploit this vulnerability to inject properties into JavaScript object prototypes, potentially leading to remote code execution, denial of service, or other security impacts.

Critical Impact

This Prototype Pollution vulnerability can allow attackers to modify the behavior of the application by injecting malicious properties into Object.prototype, potentially compromising application integrity and enabling arbitrary code execution.

Affected Products

• gulpjs copy-props (versions before 2.0.5)
• Node.js applications using the vulnerable copy-props package
• Java applications using copy-props via WebJars

Discovery Timeline

• 2021-03-23 - CVE CVE-2020-28503 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-28503

Vulnerability Analysis

This vulnerability exists in the main functionality of the copy-props package, which is designed to copy properties from one object to another. The root cause lies in insufficient validation of property keys during the copy operation, allowing an attacker to inject properties like __proto__, constructor, or prototype into the destination object.

When the copy-props function processes user-controlled input without properly sanitizing property names, it fails to block special JavaScript prototype properties. This allows an attacker to pollute the prototype chain, which affects all objects that inherit from the modified prototype.

The network-accessible attack vector means this vulnerability can be exploited remotely without requiring authentication or user interaction. Applications that pass untrusted user input to the copy-props function are at risk.

Root Cause

The vulnerability stems from the lack of property key validation in the copy-props main functionality. The package does not check whether property keys being copied are special JavaScript prototype properties (__proto__, constructor.prototype, etc.) before performing the copy operation. This oversight allows malicious property assignments to propagate to Object.prototype.

Attack Vector

The attack is network-based and requires no privileges or user interaction. An attacker can craft a malicious object containing prototype pollution payloads and pass it to an application function that uses copy-props. The vulnerability can be exploited by:

1. Identifying an application endpoint that accepts object input processed by copy-props
2. Crafting a payload with __proto__ properties containing malicious values
3. Submitting the payload to pollute the application's prototype chain
4. Leveraging the polluted prototype to achieve code execution, bypass security controls, or cause denial of service

The attack exploits the copy-props function by passing objects with specially crafted properties like {"__proto__": {"polluted": true}}. When this object is processed, the polluted property becomes accessible on all JavaScript objects in the application, which can be leveraged for further exploitation depending on how the application handles object properties.

Detection Methods for CVE-2020-28503

Indicators of Compromise

• Unexpected properties appearing on JavaScript objects that were not explicitly assigned
• Application behavior changes indicating prototype chain modifications
• Error logs showing unexpected property access or type coercion issues
• Anomalous HTTP requests containing __proto__, constructor, or prototype in JSON payloads

Detection Strategies

• Implement dependency scanning tools (npm audit, Snyk) to identify vulnerable copy-props versions in your codebase
• Monitor application logs for JSON payloads containing prototype pollution indicators (__proto__, constructor.prototype)
• Deploy Web Application Firewalls (WAF) with rules to detect and block prototype pollution payloads
• Use runtime application self-protection (RASP) solutions to detect prototype modifications at runtime

Monitoring Recommendations

• Configure SIEM rules to alert on HTTP requests containing prototype pollution patterns in request bodies
• Implement application-level logging to track object property assignments in sensitive code paths
• Enable Node.js process monitoring to detect unexpected prototype chain modifications
• Review dependency trees regularly for outdated packages with known vulnerabilities

How to Mitigate CVE-2020-28503

Immediate Actions Required

• Upgrade copy-props to version 2.0.5 or later immediately
• Audit applications for any usage of the vulnerable copy-props package
• Implement input validation to filter out __proto__ and constructor properties before passing data to object copying functions
• Consider using Object.create(null) for objects that store untrusted user input

Patch Information

The vulnerability has been addressed in copy-props version 2.0.5. The fix is available via the official GitHub pull request. Users should update their package.json to require copy-props version >=2.0.5 and run npm update or yarn upgrade to apply the fix.

For detailed vulnerability tracking information, refer to the Snyk JavaScript vulnerability report or the Snyk Java WebJars vulnerability report.

Workarounds

• Implement a wrapper function that filters out dangerous properties (__proto__, constructor, prototype) before calling copy-props
• Use Object.freeze(Object.prototype) to prevent prototype modifications (may break some legitimate functionality)
• Validate all user input on the server side before processing with object manipulation functions
• Consider alternative packages with built-in prototype pollution protection until you can upgrade

# Upgrade copy-props to patched version
npm install copy-props@^2.0.5

# Or update package.json and run
npm update copy-props

# Verify installed version
npm list copy-props