CVE-2020-9432
📋 TL;DR
CVE-2020-9432 is a certificate validation bypass vulnerability in lua-openssl's openssl_x509_check_host function. It mishandles non-boolean return values, potentially allowing attackers to spoof SSL/TLS certificates and perform man-in-the-middle attacks. This affects systems using lua-openssl 0.7.7-1 for certificate validation.
💻 Affected Systems
- lua-openssl
📦 What is this software?
Lua Openssl by Lua Openssl Project
⚠️ Risk & Real-World Impact
Worst Case
Complete SSL/TLS certificate validation bypass enabling man-in-the-middle attacks, credential theft, and data interception for all encrypted communications.
Likely Case
Attackers could spoof legitimate certificates to intercept sensitive data or impersonate trusted services.
If Mitigated
With proper network segmentation and certificate pinning, impact is limited to specific applications using vulnerable lua-openssl.
🎯 Exploit Status
The vulnerability is in a widely used cryptographic library function, making exploitation straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in commit a6dc186dd4b6b9e329a93cca3e7e3cfccfdf3cca and later versions
Vendor Advisory: https://github.com/zhaozg/lua-openssl/commit/a6dc186dd4b6b9e329a93cca3e7e3cfccfdf3cca
Restart Required: Yes
Instructions:
1. Update lua-openssl to version after commit a6dc186dd4b6b9e329a93cca3e7e3cfccfdf3cca. 2. Restart all services using lua-openssl. 3. Verify certificate validation is functioning correctly.
🔧 Temporary Workarounds
Disable vulnerable function
allTemporarily disable or avoid using openssl_x509_check_host function in lua scripts
-- Modify lua scripts to use alternative certificate validation methods
Network segmentation
linuxIsolate systems using vulnerable lua-openssl from untrusted networks
iptables -A INPUT -p tcp --dport [PORT] -s [TRUSTED_NETWORK] -j ACCEPT
iptables -A INPUT -p tcp --dport [PORT] -j DROP
🧯 If You Can't Patch
- Implement certificate pinning to hardcode trusted certificate fingerprints
- Use network monitoring to detect abnormal certificate validation patterns
🔍 How to Verify
Check if Vulnerable:
Check lua-openssl version: lua -e 'print(require("openssl").version())' and verify if it's 0.7.7-1Check Version:
lua -e 'print(require("openssl").version())'Verify Fix Applied:
Verify version is updated and test certificate validation with known bad certificates📡 Detection & Monitoring
Log Indicators:
- Unexpected certificate validation failures
- Multiple certificate validation attempts from single source
Network Indicators:
- SSL/TLS handshake anomalies
- Unexpected certificate chain presentations
SIEM Query:
source="*ssl*" AND (certificate_validation="failed" OR certificate_mismatch="true")