CVE-2020-14936
📋 TL;DR
A critical buffer overflow vulnerability in Contiki-NG's SNMP agent allows remote attackers to overwrite memory regions beyond allocated buffers by sending crafted SNMP requests. This affects IoT devices running Contiki-NG 4.4 through 4.5 with SNMP enabled, potentially enabling remote code execution or device compromise.
💻 Affected Systems
- Contiki-NG
📦 What is this software?
Contiki Ng by Contiki Ng
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attacker gains full control of IoT device, executes arbitrary code, pivots to internal networks, or bricks devices permanently.
Likely Case
Remote attacker crashes SNMP service causing denial of service, or gains limited code execution to compromise device functionality.
If Mitigated
With SNMP disabled or network segmentation, impact limited to denial of service if SNMP service crashes.
🎯 Exploit Status
Proof-of-concept details available in GitHub issue. Crafting malicious SNMP packets requires understanding of SNMP protocol but tools exist.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Contiki-NG 4.6 and later
Vendor Advisory: https://github.com/contiki-ng/contiki-ng/issues/1351
Restart Required: Yes
Instructions:
1. Update Contiki-NG to version 4.6 or later. 2. Recompile and redeploy firmware to affected IoT devices. 3. Restart devices to apply new firmware.
🔧 Temporary Workarounds
Disable SNMP Agent
allDisable SNMP functionality if not required for device operation.
Modify Contiki-NG configuration to disable SNMP agent during compilation
Network Segmentation
linuxRestrict SNMP access to trusted management networks only.
iptables -A INPUT -p udp --dport 161 -s TRUSTED_NETWORK -j ACCEPT
iptables -A INPUT -p udp --dport 161 -j DROP
🧯 If You Can't Patch
- Disable SNMP agent completely in device configuration
- Implement strict network ACLs to block all SNMP traffic (UDP port 161) to affected devices
🔍 How to Verify
Check if Vulnerable:
Check Contiki-NG version: if between 4.4-4.5 and SNMP is enabled, device is vulnerable.Check Version:
Check firmware version or Contiki-NG build configuration for version numberVerify Fix Applied:
Verify Contiki-NG version is 4.6 or later and SNMP functions properly without crashes.📡 Detection & Monitoring
Log Indicators:
- SNMP service crashes
- Memory corruption errors in system logs
- Unusual SNMP request patterns
Network Indicators:
- Malformed SNMP packets to UDP port 161
- SNMP requests with unusually long OIDs
SIEM Query:
source_port=161 AND (packet_size>1500 OR pattern_match("malformed_oid_pattern"))