CVE-2020-27009
📋 TL;DR
This vulnerability allows attackers to execute arbitrary code or cause denial-of-service by exploiting improper validation of DNS pointer offsets during domain name record decompression. It affects Siemens building automation controllers (APOGEE PXC, TALON TC) and Nucleus NET/Source Code products. An attacker needs network access to vulnerable devices to exploit this.
💻 Affected Systems
- APOGEE PXC Compact (BACnet)
- APOGEE PXC Compact (P2 Ethernet)
- APOGEE PXC Modular (BACnet)
- APOGEE PXC Modular (P2 Ethernet)
- Nucleus NET
- Nucleus Source Code
- TALON TC Compact (BACnet)
- TALON TC Modular (BACnet)
📦 What is this software?
Nucleus Net by Siemens
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with system-level privileges leading to complete device compromise, lateral movement within building automation networks, and potential physical safety impacts.
Likely Case
Denial-of-service causing building automation system disruption, HVAC failures, or access control system malfunctions.
If Mitigated
Limited impact with proper network segmentation and DNS filtering preventing malicious DNS responses from reaching vulnerable devices.
🎯 Exploit Status
Exploitation requires ability to send malicious DNS responses to vulnerable devices, which typically means having network access or compromising DNS infrastructure. No public exploits have been documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: APOGEE PXC/TALON TC (BACnet): V3.5.5 or later; APOGEE PXC (P2 Ethernet): V2.8.20 or later; Nucleus NET: V5.2 or later
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-180579.pdf
Restart Required: Yes
Instructions:
1. Download firmware updates from Siemens Industrial Security. 2. Backup device configuration. 3. Apply firmware update following Siemens documentation. 4. Verify update completion and restore configuration if needed. 5. Test system functionality.
🔧 Temporary Workarounds
Network Segmentation
allIsolate building automation controllers from general corporate networks and restrict DNS traffic to trusted servers only.
DNS Filtering
allImplement DNS response filtering at network perimeter to block malformed DNS packets before they reach vulnerable devices.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable devices from untrusted networks
- Deploy intrusion detection systems to monitor for DNS-based attacks and anomalous network traffic
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via Siemens Desigo CC, APOGEE PC, or device web interface and compare against patched versions.Check Version:
Device-specific: Use Siemens management software or access device web interface to view firmware version.Verify Fix Applied:
Confirm firmware version shows V3.5.5 or later (BACnet) or V2.8.20 or later (P2 Ethernet) for affected products.📡 Detection & Monitoring
Log Indicators:
- DNS query failures
- Device crash/restart logs
- Unusual DNS response patterns in network logs
Network Indicators:
- Malformed DNS responses to building automation controllers
- DNS packets with unusual pointer offset values
SIEM Query:
DNS response size > 512 bytes AND destination IP in building_automation_subnet AND contains pointer compression bytes