CVE-2020-12141 – CVE-2020-12141 is an out-of-bounds read vulnera... (How to Fix)

Q: What is the severity of CVE-2020-12141?

CVE-2020-12141 has a CVSS score of 9.1 (CRITICAL). CVE-2020-12141 is an out-of-bounds read vulnerability in the SNMP stack of Contiki-NG, an operating system for IoT devices. Attackers can send crafted SNMP packets to cause denial of service and potentially leak memory contents. This affects all systems running Contiki-NG 4.4 and earlier with SNMP enabled.

📋 TL;DR

CVE-2020-12141 is an out-of-bounds read vulnerability in the SNMP stack of Contiki-NG, an operating system for IoT devices. Attackers can send crafted SNMP packets to cause denial of service and potentially leak memory contents. This affects all systems running Contiki-NG 4.4 and earlier with SNMP enabled.

💻 Affected Systems

Products:

Contiki-NG

Versions: 4.4 and earlier

Operating Systems: Contiki-NG

Default Config Vulnerable: ⚠️ Yes

Notes: Only vulnerable if SNMP is enabled. Many IoT devices use Contiki-NG as their embedded OS.

📦 What is this software?

Contiki Ng by Contiki Ng

View all CVEs affecting Contiki Ng →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to complete device compromise, though this requires specific memory layouts and is less likely than DoS/information disclosure.

🟠

Likely Case

Denial of service (device crash/reboot) and potential information disclosure from memory reads.

🟢

If Mitigated

Minimal impact if SNMP is disabled or network access is restricted.

🌐 Internet-Facing: HIGH - SNMP is often exposed on IoT devices and exploitation requires no authentication.

🏢 Internal Only: MEDIUM - Still concerning for internal IoT networks but requires network access.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Proof-of-concept code exists in GitHub commits. Exploitation requires sending crafted SNMP packets to vulnerable devices.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Contiki-NG 4.5 and later

Vendor Advisory: https://github.com/contiki-ng/contiki-ng/commit/12c824386ab60de757de5001974d73b32e19ad71

Restart Required: Yes

Instructions:

1. Update Contiki-NG to version 4.5 or later. 2. Rebuild and redeploy firmware to affected devices. 3. Restart devices to apply the update.

🔧 Temporary Workarounds

Disable SNMP service

all

Disable the SNMP stack if not required for device functionality.

Modify Contiki-NG configuration to disable SNMP (exact method depends on device implementation)

Network segmentation and filtering

linux

Restrict SNMP traffic to trusted networks only.

iptables -A INPUT -p udp --dport 161 -j DROP
firewall-cmd --permanent --add-rich-rule='rule protocol value="udp" drop'

🧯 If You Can't Patch

Segment IoT devices on isolated networks with strict firewall rules blocking SNMP from untrusted sources.
Implement network monitoring for anomalous SNMP traffic patterns and device crashes.

🔍 How to Verify

Check if Vulnerable:

Check Contiki-NG version: if running 4.4 or earlier with SNMP enabled, device is vulnerable.

Check Version:

Check device firmware version or Contiki-NG build configuration (device-specific)

Verify Fix Applied:

Verify Contiki-NG version is 4.5 or later and check that the snmp_ber_decode_string_len_buffer function includes bounds checking.

📡 Detection & Monitoring

Log Indicators:

Device crash/reboot logs
SNMP service failure messages
Memory access violation errors

Network Indicators:

Malformed SNMP packets to port 161/UDP
Unusual SNMP traffic patterns from untrusted sources

SIEM Query:

source_port=161 AND (packet_size>1500 OR protocol_anomaly=snmp)

📊 Metadata

CVE ID: CVE-2020-12141

CVSS v3 Score: 9.1 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

CWE: CWE-125

Published: October 19, 2021

Last Updated: November 21, 2024

🔗 References

https://github.com/contiki-ng/contiki-ng/commit/12c824386ab60de757de5001974d73b32e19ad71#diff-32367fad664c6118fd5dda77cdf38eedc006cdd7544eca5bbeebe0b99653f8a0 Patch,Third Party Advisory
https://github.com/contiki-ng/contiki-ng/pull/1355 Patch,Third Party Advisory
https://twitter.com/ScepticCtf Third Party Advisory
https://github.com/contiki-ng/contiki-ng/commit/12c824386ab60de757de5001974d73b32e19ad71#diff-32367fad664c6118fd5dda77cdf38eedc006cdd7544eca5bbeebe0b99653f8a0 Patch,Third Party Advisory
https://github.com/contiki-ng/contiki-ng/pull/1355 Patch,Third Party Advisory
https://twitter.com/ScepticCtf Third Party Advisory

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🔗 Related Vulnerabilities

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