CVE-2021-26505
📋 TL;DR
A prototype pollution vulnerability in hello.js version 1.18.6 allows attackers to modify JavaScript object prototypes, potentially leading to arbitrary code execution. This affects any application using the vulnerable hello.js library for OAuth authentication. Attackers can exploit this remotely without authentication.
💻 Affected Systems
- hello.js
📦 What is this software?
Hello.js by Hello.js Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Application compromise allowing data manipulation, privilege escalation, and potential access to sensitive user information.
If Mitigated
Limited impact with proper input validation and sandboxing, potentially only causing application instability.
🎯 Exploit Status
Exploitation requires sending specially crafted payloads to applications using the vulnerable library. Proof-of-concept code is publicly available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.18.7 and later
Vendor Advisory: https://github.com/MrSwitch/hello.js/issues/634
Restart Required: Yes
Instructions:
1. Update hello.js to version 1.18.7 or later using npm update hello.js. 2. Restart any applications using hello.js. 3. Verify the update was successful.
🔧 Temporary Workarounds
Input validation wrapper
allImplement strict input validation for all data passed to hello.utils.extend function
Library replacement
allTemporarily replace hello.js with alternative OAuth library until patched
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) to limit script execution
- Use web application firewall (WAF) rules to block prototype pollution payloads
🔍 How to Verify
Check if Vulnerable:
Check package.json or node_modules/hello.js/package.json for version 1.18.6Check Version:
npm list hello.js | grep hello.jsVerify Fix Applied:
Verify hello.js version is 1.18.7 or higher using npm list hello.js📡 Detection & Monitoring
Log Indicators:
- Unusual OAuth callback patterns
- Multiple failed authentication attempts with malformed parameters
- Application errors related to object prototype modifications
Network Indicators:
- HTTP requests with unusual parameter structures targeting OAuth endpoints
- Payloads containing __proto__ or constructor properties
SIEM Query:
source="web_logs" AND (uri_path="/oauth*" OR uri_path="/auth*") AND (http_params CONTAINS "__proto__" OR http_params CONTAINS "constructor")