CVE-2020-24340
📋 TL;DR
This vulnerability in picoTCP and picoTCP-NG allows attackers to cause denial-of-service through out-of-bounds memory reads and invalid pointer dereferences by sending specially crafted DNS packets. It affects systems using these embedded TCP/IP stacks through version 1.7.0. The vulnerability is triggered when processing mDNS responses without proper bounds checking.
💻 Affected Systems
- picoTCP
- picoTCP-NG
📦 What is this software?
Picotcp by Altran
⚠️ Risk & Real-World Impact
Worst Case
Complete system crash or device reboot due to invalid memory access, potentially leading to persistent denial-of-service for embedded devices.
Likely Case
Service disruption or device instability when malicious DNS packets are processed, requiring manual intervention to restore functionality.
If Mitigated
Minimal impact with proper network segmentation and packet filtering preventing malicious DNS traffic from reaching vulnerable systems.
🎯 Exploit Status
Exploitation requires sending specially crafted DNS packets to vulnerable systems, which is straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 1.7.0
Vendor Advisory: https://us-cert.cisa.gov/ics/advisories/icsa-20-343-01
Restart Required: Yes
Instructions:
1. Check current picoTCP/picoTCP-NG version. 2. Update to version after 1.7.0. 3. Recompile and redeploy affected firmware. 4. Restart affected devices.
🔧 Temporary Workarounds
Disable mDNS functionality
allDisable multicast DNS functionality if not required for device operation
# Requires firmware modification to disable PICO_SUPPORT_MDNS
Network segmentation and filtering
linuxBlock mDNS traffic (port 5353) from untrusted networks
iptables -A INPUT -p udp --dport 5353 -j DROP
iptables -A INPUT -p tcp --dport 5353 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable devices from untrusted networks
- Deploy network intrusion prevention systems to detect and block malicious DNS packets
🔍 How to Verify
Check if Vulnerable:
Check firmware version and verify if picoTCP/picoTCP-NG version is 1.7.0 or earlierCheck Version:
# Check build configuration for PICO_VERSION or examine source code headersVerify Fix Applied:
Verify updated to version after 1.7.0 and test mDNS functionality with valid packets📡 Detection & Monitoring
Log Indicators:
- System crashes
- Unexpected reboots
- Memory access violation errors
Network Indicators:
- Unusual mDNS traffic patterns
- Malformed DNS packets to port 5353
SIEM Query:
source_port=5353 AND (packet_size>512 OR dns_response_count>10)