CVE-2020-7608: Yargs-parser Prototype Pollution Vulnerability

CVE-2020-7608 Overview

CVE-2020-7608 is a Prototype Pollution vulnerability affecting the yargs-parser package, a popular command-line argument parsing library for Node.js applications. The vulnerability allows attackers to trick yargs-parser into adding or modifying properties of Object.prototype using a specially crafted __proto__ payload.

Critical Impact

Attackers can manipulate the Object prototype chain to inject malicious properties that affect all objects in the JavaScript runtime, potentially leading to property injection, denial of service, or in some cases, remote code execution depending on how the application uses the polluted properties.

Affected Products

• yargs-parser for Node.js (versions prior to patched releases)

Discovery Timeline

• 2020-03-16 - CVE-2020-7608 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-7608

Vulnerability Analysis

This vulnerability is classified as Prototype Pollution (CWE-1321), a class of security issues specific to JavaScript applications. In JavaScript, all objects inherit properties from Object.prototype. When user-controlled input can modify this prototype, it creates a condition where attackers can inject arbitrary properties that will be inherited by all objects in the application.

The yargs-parser library parses command-line arguments and converts them into a JavaScript object for easier consumption by applications. Due to insufficient input validation, the parser does not properly sanitize property names that could modify the prototype chain, specifically the __proto__ property accessor.

Root Cause

The root cause of this vulnerability lies in the improper handling of object property assignments during argument parsing. When yargs-parser processes command-line arguments, it dynamically creates properties on an object based on argument names. The library failed to filter or sanitize special JavaScript properties like __proto__, constructor, and prototype that provide access to the prototype chain.

When an attacker supplies an argument with a name like __proto__.maliciousProperty, the parser follows the prototype chain and sets properties on Object.prototype rather than the intended argument object.

Attack Vector

This is a local attack vector vulnerability that requires the attacker to control input passed to yargs-parser. The attack is executed by supplying specially crafted command-line arguments or configuration that include prototype-polluting payloads.

An attacker could exploit this by passing arguments in the format --__proto__.polluted=true or using nested object notation like --constructor.prototype.polluted=true. When the application parses these arguments, the malicious properties are added to the Object prototype, affecting all objects created after the pollution occurs.

The exploitation technique involves providing argument strings that traverse the prototype chain. For detailed technical analysis and proof-of-concept information, see the Snyk Vulnerability Report.

Detection Methods for CVE-2020-7608

Indicators of Compromise

• Unexpected properties appearing on JavaScript objects that were not explicitly defined
• Application behavior changes after processing user-supplied command-line arguments
• Presence of properties like polluted, isAdmin, or other suspicious names on Object.prototype
• Anomalous application crashes or logic errors following argument parsing operations

Detection Strategies

• Implement Software Composition Analysis (SCA) scanning to identify vulnerable versions of yargs-parser in your dependency tree
• Monitor for unusual property access patterns in runtime application monitoring
• Use static analysis tools to detect prototype pollution sinks in code that uses yargs-parser
• Review npm audit reports for known vulnerabilities in transitive dependencies

Monitoring Recommendations

• Enable detailed logging of command-line arguments passed to Node.js applications
• Implement runtime object monitoring to detect unexpected prototype modifications
• Set up alerts for npm audit findings related to prototype pollution vulnerabilities
• Monitor application logs for TypeError exceptions that may indicate prototype pollution side effects

How to Mitigate CVE-2020-7608

Immediate Actions Required

• Update yargs-parser to the latest patched version using npm update yargs-parser
• Audit your dependency tree with npm audit to identify vulnerable transitive dependencies
• Review applications using yargs-parser to assess potential exposure
• Consider implementing Object.freeze on critical prototypes as a defense-in-depth measure

Patch Information

The vulnerability has been addressed by the yargs maintainers. Organizations should update to the patched versions of yargs-parser. For specific version information and remediation guidance, refer to the Snyk Vulnerability Report.

Use npm audit fix to automatically update to patched versions where possible, or manually specify the updated version in your package.json dependencies.

Workarounds

• Sanitize user input before passing to yargs-parser by filtering out __proto__, constructor, and prototype property names
• Use Object.create(null) to create objects without prototype inheritance where applicable
• Implement a wrapper function that validates argument names before processing
• Consider using alternative argument parsing libraries that include prototype pollution protections

# Check for vulnerable yargs-parser versions
npm audit --production

# Update yargs-parser to latest version
npm update yargs-parser

# If using yarn
yarn upgrade yargs-parser