CVE-2021-42143
📋 TL;DR
This vulnerability in Contiki-NG tinyDTLS allows remote attackers to cause denial of service and potentially leak sensitive information by sending a malformed ClientHello handshake message. The infinite loop consumes all resources, while the buffer over-read can disclose memory contents. Systems using affected versions of Contiki-NG with tinyDTLS enabled are vulnerable.
💻 Affected Systems
- Contiki-NG
📦 What is this software?
Tinydtls by Contiki Ng
⚠️ Risk & Real-World Impact
Worst Case
Complete system resource exhaustion leading to denial of service, plus potential disclosure of sensitive memory contents including cryptographic keys or other secrets.
Likely Case
Denial of service through resource exhaustion, potentially disrupting IoT/embedded device functionality.
If Mitigated
Limited impact if network controls prevent malicious traffic or if the vulnerable component is not exposed.
🎯 Exploit Status
The vulnerability requires sending a specially crafted ClientHello message with odd-length cipher suites. Exploitation is straightforward once the malformed packet is constructed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after commit 53a0d97
Vendor Advisory: https://github.com/contiki-ng/contiki-ng/security/advisories
Restart Required: Yes
Instructions:
1. Update Contiki-NG to latest version. 2. Rebuild and redeploy affected firmware. 3. Restart devices/services using the updated firmware.
🔧 Temporary Workarounds
Disable tinyDTLS
allIf DTLS functionality is not required, disable tinyDTLS in Contiki-NG configuration
Modify project configuration to set DTLS=0 or similar
Network filtering
linuxBlock or filter DTLS traffic to vulnerable devices
iptables -A INPUT -p udp --dport 5684 -j DROP
Configure firewall to block UDP port 5684 (CoAPs default)
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable devices
- Deploy intrusion prevention systems to detect and block malformed DTLS packets
🔍 How to Verify
Check if Vulnerable:
Check Contiki-NG version and tinyDTLS configuration. If using tinyDTLS and version is before fix commit 53a0d97, system is vulnerable.Check Version:
Check Contiki-NG git commit hash or version in source/build configurationVerify Fix Applied:
Verify Contiki-NG version is updated beyond commit 53a0d97 and test DTLS handshake functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual resource consumption
- DTLS handshake failures
- System crashes or hangs
Network Indicators:
- Malformed DTLS ClientHello packets with odd-length cipher suites
- Unusual UDP traffic to DTLS ports
SIEM Query:
source="network" AND (protocol="DTLS" OR port=5684) AND packet_size_odd=true