CVE-2023-3696: Mongoosejs Mongoose Prototype Pollution

CVE-2023-3696 Overview

CVE-2023-3696 is a critical Prototype Pollution vulnerability affecting the Mongoose ODM (Object Document Mapper) library for MongoDB and Node.js. This vulnerability exists in versions of Mongoose prior to 7.3.4 and allows attackers to manipulate the JavaScript Object prototype, potentially leading to remote code execution, denial of service, or authentication bypass in affected applications.

Prototype Pollution is a JavaScript-specific vulnerability class (CWE-1321) that occurs when attackers can inject properties into object prototypes. Since all JavaScript objects inherit from Object.prototype, polluting this prototype can have application-wide consequences, affecting every object in the runtime environment.

Critical Impact

Successful exploitation of this prototype pollution vulnerability can allow unauthenticated remote attackers to modify application behavior, bypass security controls, or achieve remote code execution through specially crafted input targeting the Mongoose document initialization process.

Affected Products

• mongoosejs mongoose versions prior to 7.3.4
• Applications using Mongoose ODM for Node.js and MongoDB
• Node.js applications with user-controlled input processed through Mongoose schemas

Discovery Timeline

• 2023-07-17 - CVE CVE-2023-3696 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-3696

Vulnerability Analysis

The vulnerability exists in Mongoose's document initialization function within lib/document.js. When processing document data, the _init function iterates over object keys without properly validating whether these keys correspond to dangerous prototype properties. This allows attackers to inject __proto__ or constructor as keys in document data, which can pollute the Object prototype when processed.

Prototype pollution attacks are particularly dangerous in Node.js applications because:

1. Global Impact: Modifications to Object.prototype affect all objects in the application
2. Persistence: Polluted properties remain until the application restarts
3. Chain Attacks: Prototype pollution can enable secondary attacks like remote code execution when combined with certain gadgets in the application or its dependencies

Root Cause

The root cause of this vulnerability is insufficient input validation in Mongoose's document initialization logic. The _init function failed to sanitize property names before using them to set values on document objects. Specifically, the code did not check for and reject reserved JavaScript prototype properties (__proto__ and constructor) when iterating through keys during document initialization.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending specially crafted JSON data to an application endpoint that processes the data through Mongoose. When the malicious document containing __proto__ or constructor properties is initialized, the prototype pollution occurs.

The security patch adds explicit checks to prevent prototype pollution:

 
   function _init(index) {
     i = keys[index];
+    // avoid prototype pollution
+    if (i === '__proto__' || i === 'constructor') {
+      return;
+    }
     path = prefix + i;
     schemaType = docSchema.path(path);
 

Source: GitHub Mongoose Commit

Detection Methods for CVE-2023-3696

Indicators of Compromise

• Unexpected properties appearing on objects throughout the application
• Application behavior changes without code modifications
• Anomalous authentication bypasses or privilege escalations
• HTTP requests containing __proto__ or constructor in JSON payloads
• Unexplained crashes or errors related to object property access

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block requests containing __proto__ or constructor in JSON bodies
• Enable application-level logging to capture incoming request payloads for forensic analysis
• Deploy runtime application self-protection (RASP) solutions that can detect prototype pollution attempts
• Monitor for unexpected object property access patterns in application logs

Monitoring Recommendations

• Set up alerts for HTTP requests containing prototype pollution payloads (__proto__, constructor.prototype)
• Monitor application error logs for TypeError exceptions related to unexpected object properties
• Implement dependency vulnerability scanning in CI/CD pipelines to detect vulnerable Mongoose versions
• Use SentinelOne Singularity to monitor Node.js application runtime behavior for anomalous prototype modifications

How to Mitigate CVE-2023-3696

Immediate Actions Required

• Upgrade Mongoose to version 7.3.4 or later immediately
• Audit all application endpoints that accept user-controlled JSON input
• Implement input validation to reject objects containing __proto__ or constructor properties
• Review application dependencies for other prototype pollution vulnerabilities
• Consider using Object.freeze(Object.prototype) as a temporary defensive measure in non-production environments

Patch Information

The vulnerability has been addressed in Mongoose version 7.3.4. The fix adds explicit checks in the _init function to skip processing of __proto__ and constructor keys, preventing prototype pollution during document initialization.

For detailed patch information, see the GitHub Mongoose Commit and the Huntr Bounty Report.

Workarounds

• Implement middleware to sanitize all incoming JSON data, removing __proto__ and constructor properties before processing
• Use JSON.parse() with a reviver function that filters dangerous keys
• Apply strict schema validation to reject documents with unexpected properties
• Consider using Object.create(null) for objects that will be populated with user data

# Update Mongoose to patched version
npm update mongoose@7.3.4

# Or install specific patched version
npm install mongoose@^7.3.4

# Verify installed version
npm list mongoose