CVE-2020-25107
📋 TL;DR
This vulnerability in Ethernut's DNS implementation lacks proper null-termination checks for domain names, allowing attackers to trigger buffer overflows. This affects systems running Nut/OS 5.1 with DNS functionality enabled, potentially leading to denial-of-service or remote code execution.
💻 Affected Systems
- Ethernut
- Nut/OS
📦 What is this software?
Nut\/os by Ethernut
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise and attacker persistence
Likely Case
Denial-of-service causing DNS service disruption and system instability
If Mitigated
Limited impact with proper network segmentation and input validation
🎯 Exploit Status
DNS protocol is typically unauthenticated, making exploitation straightforward if vulnerable systems are accessible
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Nut/OS 5.2 or later
Vendor Advisory: https://www.ethernut.de/en/download/
Restart Required: Yes
Instructions:
1. Download Nut/OS 5.2 or later from official source. 2. Replace existing Nut/OS installation. 3. Recompile affected applications. 4. Restart systems.
🔧 Temporary Workarounds
Disable DNS functionality
allDisable DNS services if not required for system operation
Modify Nut/OS configuration to disable DNS module
Network segmentation
linuxRestrict network access to DNS services
iptables -A INPUT -p udp --dport 53 -j DROP
iptables -A INPUT -p tcp --dport 53 -j DROP
🧯 If You Can't Patch
- Implement network-level DNS filtering and monitoring
- Deploy intrusion detection systems to monitor for DNS exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check Nut/OS version and verify DNS functionality is enabledCheck Version:
Check Nut/OS build configuration or version header filesVerify Fix Applied:
Verify Nut/OS version is 5.2 or later and test DNS functionality📡 Detection & Monitoring
Log Indicators:
- DNS query failures
- System crashes after DNS queries
- Unusual DNS request patterns
Network Indicators:
- Malformed DNS packets
- Excessive DNS traffic to vulnerable systems
SIEM Query:
source="dns" AND (packet_size>512 OR contains(query,"\x00"))