CVE-2021-34433
📋 TL;DR
This vulnerability in Eclipse Californium allows attackers to bypass certificate verification during DTLS handshakes, enabling man-in-the-middle attacks. It affects clients using certificate-based authentication (x509 or RPK) with vulnerable versions, potentially compromising secure communications.
💻 Affected Systems
- Eclipse Californium
📦 What is this software?
Californium by Eclipse
Californium by Eclipse
Californium by Eclipse
Californium by Eclipse
⚠️ Risk & Real-World Impact
Worst Case
Attackers can intercept and manipulate encrypted DTLS communications, potentially stealing sensitive data or injecting malicious content into secure channels.
Likely Case
Man-in-the-middle attacks against DTLS-secured CoAP communications, allowing eavesdropping on IoT device communications.
If Mitigated
Limited impact if network segmentation prevents MITM positioning or if additional authentication layers are used.
🎯 Exploit Status
Exploitation requires network positioning for MITM attacks. No authentication needed to exploit the verification bypass.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.6.5 and 3.0.0-M4
Vendor Advisory: https://bugs.eclipse.org/bugs/show_bug.cgi?id=575281
Restart Required: Yes
Instructions:
1. Update Eclipse Californium to version 2.6.5 or 3.0.0-M4. 2. Restart affected services. 3. Verify certificate verification is now enforced.
🔧 Temporary Workarounds
Disable certificate-based DTLS
allSwitch to PSK-based DTLS handshakes which are not affected by this vulnerability
Configure CoAP/DTLS to use PSK instead of x509/RPK certificates
Network segmentation
allIsolate vulnerable systems to prevent MITM positioning
Implement VLAN segmentation
Use firewall rules to restrict DTLS traffic
🧯 If You Can't Patch
- Implement network monitoring for DTLS handshake anomalies
- Use additional application-layer authentication mechanisms
🔍 How to Verify
Check if Vulnerable:
Check Californium version: if between 2.0.0-2.6.4 or 3.0.0-M1-3.0.0-M3 and using certificate-based DTLS, system is vulnerable.Check Version:
Check build.gradle or pom.xml for Californium dependency versionVerify Fix Applied:
Verify version is 2.6.5+ or 3.0.0-M4+. Test DTLS handshake with invalid server certificate - should fail.📡 Detection & Monitoring
Log Indicators:
- DTLS handshake successes with invalid certificates
- Certificate verification warnings/errors
Network Indicators:
- Unusual DTLS handshake patterns
- MITM detection alerts
SIEM Query:
Search for DTLS handshake events with certificate verification failures followed by successful connections