CVE-2021-25667
📋 TL;DR
A stack-based buffer overflow vulnerability in Siemens industrial network devices allows remote attackers to cause denial-of-service or potentially execute arbitrary code by sending specially crafted STP BPDU frames. Affected devices include multiple RUGGEDCOM and SCALANCE product families running vulnerable firmware versions. Successful exploitation requires the passive listening feature to be enabled on the device.
💻 Affected Systems
- RUGGEDCOM RM1224
- SCALANCE M-800
- SCALANCE S615
- SCALANCE SC-600 Family
- SCALANCE XB-200
- SCALANCE XC-200
- SCALANCE XF-200BA
- SCALANCE XM400
- SCALANCE XP-200
- SCALANCE XR-300WG
- SCALANCE XR500
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with full device compromise, allowing attacker to modify configurations, disrupt industrial operations, or pivot to other network segments.
Likely Case
Denial-of-service condition causing network disruption and potential operational downtime in industrial environments.
If Mitigated
Limited impact if passive listening feature is disabled or devices are properly segmented from untrusted networks.
🎯 Exploit Status
Exploitation requires network access to the device and passive listening to be enabled. STP BPDU manipulation requires specific network knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V6.4 for most products, V2.1.3 for SC-600, V4.1 for XB/XC/XF/XP/XR-300WG, V6.2 for XM400/XR500
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-979775.pdf
Restart Required: Yes
Instructions:
1. Download appropriate firmware update from Siemens Industrial Security Advisory. 2. Backup current configuration. 3. Apply firmware update following vendor instructions. 4. Verify successful update and restore configuration if needed.
🔧 Temporary Workarounds
Disable Passive Listening
allDisable the passive listening feature that is required for exploitation
Configure via web interface or CLI: set passive-listening disabled
Network Segmentation
allSegment affected devices from untrusted networks using firewalls or VLANs
Configure firewall rules to block STP BPDU traffic (protocol 0x42) from untrusted sources
🧯 If You Can't Patch
- Disable passive listening feature on all affected devices
- Implement strict network segmentation to isolate affected devices from potential attackers
- Monitor for STP BPDU anomalies and unauthorized traffic
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or CLI command 'show version' and compare against affected versions listCheck Version:
show versionVerify Fix Applied:
Verify firmware version is updated to patched version and passive listening is disabled📡 Detection & Monitoring
Log Indicators:
- Device crash/reboot logs
- STP protocol anomalies in system logs
- Unexpected configuration changes
Network Indicators:
- Malformed STP BPDU frames
- Unusual STP traffic patterns
- Traffic from unexpected sources to port 0x42
SIEM Query:
source="network_device" AND (protocol="STP" OR port=0x42) AND (payload_size>normal OR malformed_packet=true)