CVE-2021-25668
📋 TL;DR
This vulnerability in Siemens SCALANCE industrial switches allows attackers to send specially crafted POST requests that cause heap memory corruption. Successful exploitation could lead to denial-of-service or remote code execution on affected devices. All organizations using the listed SCALANCE switches with vulnerable firmware versions are affected.
💻 Affected Systems
- SCALANCE X200-4P IRT
- SCALANCE X201-3P IRT
- SCALANCE X201-3P IRT PRO
- SCALANCE X202-2 IRT
- SCALANCE X202-2P IRT
- SCALANCE X202-2P IRT PRO
- SCALANCE X204 IRT
- SCALANCE X204 IRT PRO
- SCALANCE X204-2
- SCALANCE X204-2FM
- SCALANCE X204-2LD
- SCALANCE X204-2LD TS
- SCALANCE X204-2TS
- SCALANCE X206-1
- SCALANCE X206-1LD
- SCALANCE X208
- SCALANCE X208PRO
- SCALANCE X212-2
- SCALANCE X212-2LD
- SCALANCE X216
- SCALANCE X224
- SCALANCE XF201-3P IRT
- SCALANCE XF202-2P IRT
- SCALANCE XF204
- SCALANCE XF204 IRT
- SCALANCE XF204-2
- SCALANCE XF204-2BA IRT
- SCALANCE XF206-1
- SCALANCE XF208
📦 What is this software?
Scalance X201 3p Irt Pro Firmware by Siemens
Scalance X202 2p Irt Pro Firmware by Siemens
Scalance Xf204 2ba Irt Firmware by Siemens
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with full device compromise, allowing attackers to disrupt industrial operations or pivot to other network segments.
Likely Case
Denial-of-service causing network disruption in industrial environments, potentially halting production processes.
If Mitigated
Limited impact if devices are behind firewalls with restricted web interface access and proper network segmentation.
🎯 Exploit Status
The vulnerability requires sending crafted POST requests to the web interface. No authentication is required, making exploitation straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 5.5.1 for IRT models, Version 5.2.5 for non-IRT models
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-187092.pdf
Restart Required: Yes
Instructions:
1. Download firmware update from Siemens Industrial Security website. 2. Backup current configuration. 3. Upload new firmware via web interface or management software. 4. Reboot device. 5. Verify firmware version after reboot.
🔧 Temporary Workarounds
Disable Web Interface
allDisable the HTTP/HTTPS web server interface if not required for operations
Configure via CLI: no ip http server
Configure via CLI: no ip http secure-server
Restrict Network Access
linuxImplement firewall rules to restrict access to web interface ports (80/443)
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Segment affected switches into isolated VLANs with strict access controls
- Implement network monitoring for anomalous POST requests to switch web interfaces
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface (System > Device Information) or CLI (show version)Check Version:
show versionVerify Fix Applied:
Confirm firmware version is 5.5.1 or higher for IRT models, or 5.2.5 or higher for non-IRT models📡 Detection & Monitoring
Log Indicators:
- Multiple failed POST requests
- Web server crash logs
- Device reboot events
Network Indicators:
- Unusual POST requests to switch web interfaces
- Traffic spikes to port 80/443 of switches
SIEM Query:
source="switch_logs" AND ("POST" AND "HTTP/1.1" AND status="500") OR ("web server" AND "crash")