CVE-2020-8203: Lodash Prototype Pollution Vulnerability

CVE-2020-8203 Overview

CVE-2020-8203 is a prototype pollution vulnerability affecting the popular JavaScript utility library Lodash. The vulnerability exists in the _.zipObjectDeep function in Lodash versions prior to 4.17.20. Prototype pollution attacks allow an attacker to inject properties into JavaScript Object prototypes, which can lead to property injection, denial of service, or in some cases remote code execution depending on how the application processes objects.

This vulnerability is particularly concerning due to Lodash's widespread use as a dependency in Node.js applications and front-end JavaScript projects. Thousands of applications rely on Lodash for common utility functions, making this a supply chain security concern with significant downstream impact.

Critical Impact

Attackers can manipulate object prototypes to inject malicious properties, potentially leading to unauthorized data modification or application denial of service across all objects in the JavaScript runtime.

Affected Products

• Lodash versions prior to 4.17.20
• Oracle Banking Corporate Lending Process Management (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Banking Credit Facilities Process Management (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Banking Extensibility Workbench (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Banking Liquidity Management (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Banking Supply Chain Finance (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Banking Trade Finance Process Management (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Banking Virtual Account Management (versions 14.2.0, 14.3.0, 14.5.0)
• Oracle Blockchain Platform
• Oracle Communications Billing and Revenue Management
• Oracle Communications Cloud Native Core Policy
• Oracle Communications Session Border Controller
• Oracle Communications Session Router
• Oracle Enterprise Communications Broker
• Oracle JD Edwards EnterpriseOne Tools
• Oracle PeopleSoft Enterprise PeopleTools (versions 8.58, 8.59)
• Oracle Primavera Gateway

Discovery Timeline

• 2020-07-15 - CVE-2020-8203 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-8203

Vulnerability Analysis

Prototype pollution is a JavaScript-specific vulnerability class that exploits the language's prototype-based inheritance model. In JavaScript, all objects inherit properties from their prototype chain, with Object.prototype sitting at the top. When an attacker can modify Object.prototype, those malicious properties become accessible on all objects within the application.

The vulnerability in Lodash's _.zipObjectDeep function allows attackers to supply crafted input that pollutes the Object.prototype. The function is designed to create objects from arrays of paths and values, supporting deep property paths using dot notation or bracket syntax. However, it fails to properly sanitize input paths that reference prototype properties like __proto__ or constructor.prototype.

When user-controlled data is passed to _.zipObjectDeep without proper validation, an attacker can inject paths such as __proto__.polluted that modify the base Object prototype rather than creating a nested property. This affects the integrity and availability of the application, as subsequently created objects may contain unexpected properties that alter application logic or cause crashes.

Root Cause

The root cause of CVE-2020-8203 lies in insufficient input validation within the _.zipObjectDeep function. The function processes property paths without checking whether they attempt to traverse or modify prototype properties. JavaScript's special __proto__ property accessor and the constructor property provide pathways to reach and modify Object.prototype, and the Lodash function did not block these dangerous paths.

The vulnerability is classified under CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes) and CWE-770 (Allocation of Resources Without Limits or Throttling). These weaknesses indicate both the prototype pollution vector and the potential for resource exhaustion attacks through unbounded object property creation.

Attack Vector

The attack requires network access to an application endpoint that processes user-supplied data through the vulnerable _.zipObjectDeep function. An attacker crafts malicious input containing prototype-polluting property paths and submits them to the target application. The attack complexity is considered high because successful exploitation depends on finding an application code path that passes attacker-controlled data to the vulnerable function.

A typical attack scenario involves an application that uses _.zipObjectDeep to transform API request data into internal objects. The attacker sends a request with a path like ["__proto__.isAdmin"] paired with a value of true. If the application later checks someObject.isAdmin on any object, it will inherit this polluted property and return true, potentially bypassing authorization checks.

The vulnerability enables modification of object prototypes application-wide, and can cause denial of service by corrupting critical prototype properties that crash the application when accessed. For more technical details, see the HackerOne Report #712065.

Detection Methods for CVE-2020-8203

Indicators of Compromise

• HTTP requests containing __proto__, constructor, or prototype strings in JSON payloads or query parameters
• Application logs showing unexpected object property access errors or type confusion exceptions
• JavaScript runtime errors related to accessing properties on objects that should not exist
• Unusual application behavior where default values or security checks are bypassed

Detection Strategies

• Implement static analysis scanning of application dependencies using tools like npm audit or Snyk to identify vulnerable Lodash versions
• Deploy web application firewall (WAF) rules to detect and block requests containing prototype pollution patterns
• Use runtime application self-protection (RASP) solutions to monitor object prototype modifications
• Configure SentinelOne Singularity to monitor Node.js application behavior for anomalous object property access patterns

Monitoring Recommendations

• Enable detailed application logging for all endpoints that process user input through Lodash transformation functions
• Monitor npm audit output in CI/CD pipelines to catch vulnerable dependency versions before deployment
• Set up alerts for error patterns indicative of prototype pollution such as "Cannot read property of undefined" on expected objects
• Track dependency versions across the organization and alert when outdated Lodash packages are detected

How to Mitigate CVE-2020-8203

Immediate Actions Required

• Upgrade Lodash to version 4.17.20 or later across all affected applications
• Run npm audit or yarn audit to identify all projects using vulnerable Lodash versions
• Review application code to identify usages of _.zipObjectDeep and other deep property assignment functions
• Implement input validation to reject payloads containing prototype-related property paths before processing

Patch Information

The Lodash maintainers addressed this vulnerability in version 4.17.20. The fix adds safeguards to prevent modification of object prototypes through deep property assignment functions. Organizations should update their package.json dependencies and lock files to require Lodash >=4.17.20.

Oracle addressed this vulnerability across their affected products through multiple Critical Patch Updates. For Oracle products, refer to the Oracle CPU April 2021 Alert, Oracle CPU October 2021 Alert, Oracle CPU January 2022 Alert, and Oracle CPU April 2022 Alert for specific patching guidance.

Additional vendor guidance is available through the NetApp Security Advisory and the GitHub Issue Discussion.

Workarounds

• Implement input sanitization middleware to filter out __proto__, constructor, and prototype strings from all user input before processing
• Use Object.freeze on Object.prototype at application startup to prevent prototype modifications (note: may break some legitimate functionality)
• Replace vulnerable Lodash functions with safer alternatives or native JavaScript methods where possible
• Isolate processing of untrusted input in separate JavaScript contexts or worker threads to contain potential prototype pollution

# Update Lodash to patched version
npm update lodash@4.17.20

# Audit for vulnerable packages
npm audit --production

# Force resolution to safe version in package.json
npm pkg set resolutions.lodash=">=4.17.20"