CVE-2021-25947
📋 TL;DR
This is a prototype pollution vulnerability in the 'nestie' JavaScript library that allows attackers to modify object prototypes, potentially leading to denial of service or remote code execution. Any application using vulnerable versions of nestie is affected, particularly Node.js applications that process untrusted user input.
💻 Affected Systems
- nestie
📦 What is this software?
Nestie by Nestie Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Denial of service through application crashes or instability, with potential for limited remote code execution in specific configurations.
If Mitigated
Limited impact if input validation and sanitization prevent prototype pollution payloads from reaching vulnerable code paths.
🎯 Exploit Status
Prototype pollution vulnerabilities are well-understood with public proof-of-concepts available. Exploitation requires the application to process attacker-controlled objects through nestie functions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.0.1
Vendor Advisory: https://www.npmjs.com/advisories/1648
Restart Required: Yes
Instructions:
1. Update nestie to version 1.0.1 or later using 'npm update nestie'. 2. Restart your Node.js application. 3. Test that the update doesn't break functionality.
🔧 Temporary Workarounds
Input validation and sanitization
allImplement strict input validation to reject objects with prototype pollution payloads before they reach nestie functions.
Object.freeze() on prototypes
allFreeze Object.prototype and other relevant prototypes to prevent pollution attacks.
Object.freeze(Object.prototype);
🧯 If You Can't Patch
- Isolate the vulnerable application in a restricted network segment with minimal permissions
- Implement web application firewall (WAF) rules to block prototype pollution patterns in incoming requests
🔍 How to Verify
Check if Vulnerable:
Check package.json or run 'npm list nestie' to see if version is between 0.0.0 and 1.0.0 inclusive.Check Version:
npm list nestie | grep nestieVerify Fix Applied:
Verify nestie version is 1.0.1 or higher using 'npm list nestie' and test with known prototype pollution payloads.📡 Detection & Monitoring
Log Indicators:
- Unusual application crashes, memory errors, or unexpected property modifications in object logs
Network Indicators:
- HTTP requests containing __proto__ or constructor properties in JSON payloads
SIEM Query:
source="application_logs" AND ("__proto__" OR "constructor" OR "prototype") AND dest_port="*"