CVE-2019-18840
📋 TL;DR
This vulnerability in wolfSSL allows attackers to execute arbitrary code or cause denial of service via a specially crafted certificate during TLS handshake. It affects systems using wolfSSL 4.1.0 through 4.2.0c for TLS/SSL operations. The vulnerability is triggered during certificate parsing when connecting to malicious servers or processing client certificates.
💻 Affected Systems
- wolfSSL embedded SSL/TLS library
📦 What is this software?
Wolfssl by Wolfssl
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or persistent backdoor installation.
Likely Case
Denial of service causing TLS handshake failures and service disruption.
If Mitigated
Limited impact with proper network segmentation and certificate validation controls.
🎯 Exploit Status
Exploitation requires sending a malicious certificate during TLS handshake. Proof-of-concept exists in GitHub issues.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: wolfSSL 4.2.0d and later
Vendor Advisory: https://github.com/wolfSSL/wolfssl/issues/2555
Restart Required: Yes
Instructions:
1. Update wolfSSL to version 4.2.0d or later. 2. Recompile applications using wolfSSL. 3. Restart affected services.
🔧 Temporary Workarounds
Disable certificate parsing
allDisable certificate parsing in wolfSSL configuration if not required
Configure wolfSSL with --disable-cert or equivalent build option
🧯 If You Can't Patch
- Implement strict certificate validation and only accept certificates from trusted CAs
- Use network segmentation to isolate vulnerable systems from untrusted networks
🔍 How to Verify
Check if Vulnerable:
Check wolfSSL version with wolfSSL_version() function or check library version in build configurationCheck Version:
wolfssl-config --version or check library headersVerify Fix Applied:
Verify wolfSSL version is 4.2.0d or later and test TLS handshake with various certificates📡 Detection & Monitoring
Log Indicators:
- TLS handshake failures
- Certificate parsing errors
- Memory corruption warnings
Network Indicators:
- Unusual certificate sizes or structures in TLS traffic
SIEM Query:
search for 'wolfSSL' AND ('certificate error' OR 'handshake failure' OR 'memory corruption')