CVE-2020-7700
📋 TL;DR
CVE-2020-7700 is a prototype pollution vulnerability in phpjs's parse_str function that allows attackers to inject properties into JavaScript objects, potentially leading to remote code execution or denial of service. This affects all applications using any version of the phpjs library. The vulnerability is particularly dangerous because it can be exploited through user-controlled input.
💻 Affected Systems
- phpjs
📦 What is this software?
Php.js by Php.js 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, privilege escalation, or data manipulation through object property pollution.
If Mitigated
Limited impact if input validation and sanitization prevent malicious payloads from reaching vulnerable functions.
🎯 Exploit Status
Exploitation requires user input to reach the vulnerable parse_str function. Public proof-of-concept code demonstrates the prototype pollution technique.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: N/A
Vendor Advisory: https://snyk.io/vuln/SNYK-JS-PHPJS-598681
Restart Required: No
Instructions:
1. Remove phpjs dependency entirely. 2. Replace with alternative libraries like php-parser or custom implementations. 3. Update package.json to remove phpjs. 4. Test application functionality after removal.
🔧 Temporary Workarounds
Input Validation and Sanitization
allImplement strict input validation to prevent malicious payloads from reaching parse_str function.
Object.freeze() on Prototypes
allFreeze Object.prototype to prevent property injection.
Object.freeze(Object.prototype);
🧯 If You Can't Patch
- Implement Web Application Firewall (WAF) rules to block prototype pollution patterns
- Isolate affected applications in network segments with strict access controls
🔍 How to Verify
Check if Vulnerable:
Check package.json or package-lock.json for phpjs dependency. Run: npm list phpjs or check node_modules directory.Check Version:
npm list phpjsVerify Fix Applied:
Confirm phpjs is removed from dependencies and not present in node_modules. Run: npm list | grep phpjs (should return empty).📡 Detection & Monitoring
Log Indicators:
- Unusual property assignments to global objects
- Unexpected object modifications in application logs
- Error logs related to prototype chain pollution
Network Indicators:
- HTTP requests with specially crafted query strings or POST data containing prototype pollution patterns
SIEM Query:
source=web_logs AND (uri_query CONTAINS "__proto__" OR uri_query CONTAINS "constructor.prototype")