CVE-2021-22735
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on affected Schneider Electric homeLYnk and spaceLYnk devices by bypassing cryptographic signature verification. Attackers can copy unauthorized malicious code to the device, potentially taking full control. Organizations using these building automation systems with vulnerable firmware versions are affected.
💻 Affected Systems
- homeLYnk (Wiser For KNX)
- spaceLYnk
📦 What is this software?
Homelynk Firmware by Schneider Electric
Spacelynk Firmware by Schneider Electric
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of building automation system allowing attackers to manipulate physical controls (lighting, HVAC, security), deploy ransomware, or pivot to other network segments.
Likely Case
Remote code execution leading to device compromise, data theft, or disruption of building operations.
If Mitigated
Limited impact if devices are isolated on separate VLANs with strict network segmentation and access controls.
🎯 Exploit Status
The vulnerability description suggests remote exploitation without authentication is possible, making this relatively easy to exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after V2.60
Vendor Advisory: https://download.schneider-electric.com/files?p_Doc_Ref=SEVD-2021-130-04
Restart Required: Yes
Instructions:
1. Download updated firmware from Schneider Electric portal. 2. Backup device configuration. 3. Apply firmware update via device management interface. 4. Verify successful update and restore configuration if needed.
🔧 Temporary Workarounds
Network Segmentation
allIsolate affected devices on separate VLANs with strict firewall rules to limit attack surface.
Access Control Lists
allImplement network ACLs to restrict access to device management interfaces to authorized IPs only.
🧯 If You Can't Patch
- Segment devices on isolated network with no internet access
- Implement strict inbound/outbound firewall rules and monitor for suspicious traffic
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or SSH. If version is V2.60 or earlier, device is vulnerable.Check Version:
Check via web interface at http://[device-ip] or SSH to device and check firmware version in system settings.Verify Fix Applied:
Verify firmware version is greater than V2.60 via device management interface.📡 Detection & Monitoring
Log Indicators:
- Unauthorized firmware update attempts
- Unexpected file transfers to device
- Authentication bypass logs
Network Indicators:
- Unexpected connections to device management ports (typically 80, 443, 22)
- Suspicious file transfer patterns to device
SIEM Query:
source="device_logs" AND (event="firmware_update" OR event="file_transfer") AND result="failed" OR source="firewall" AND dest_port IN (80, 443, 22) AND dest_ip IN (affected_devices)