CVE-2020-21992
📋 TL;DR
CVE-2020-21992 allows authenticated attackers to execute arbitrary OS commands with root privileges on Inim Electronics SmartLiving SmartLAN/G/SI devices. The vulnerability exists in the web.cgi binary's testemail module where unsanitized user input is passed to system() calls. Organizations using affected SmartLiving devices with default credentials are at risk.
💻 Affected Systems
- Inim Electronics SmartLiving SmartLAN/G/SI
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to install persistent backdoors, pivot to internal networks, disrupt operations, or use device as part of botnet.
Likely Case
Attacker gains full control of vulnerable device, potentially accessing connected systems, modifying configurations, or stealing data.
If Mitigated
Limited impact if strong authentication, network segmentation, and input validation are implemented.
🎯 Exploit Status
Exploit requires authentication but default credentials are often unchanged. Command injection via 'par' parameter in POST requests to web.cgi.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: > 6.x
Vendor Advisory: https://www.zeroscience.mk/en/vulnerabilities/ZSL-2019-5544.php
Restart Required: Yes
Instructions:
1. Contact Inim Electronics for firmware update >6.x. 2. Download latest firmware. 3. Backup configuration. 4. Apply firmware update via web interface. 5. Reboot device. 6. Verify update.
🔧 Temporary Workarounds
Disable web interface
linuxDisable the vulnerable web.cgi interface if not required
rm /path/to/web.cgi
chmod 000 /path/to/web.cgi
Network segmentation
allIsolate SmartLiving devices in separate VLAN with strict firewall rules
🧯 If You Can't Patch
- Change default credentials immediately and enforce strong authentication
- Implement strict network segmentation and firewall rules to limit device access
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or SSH. If version <=6.x, device is vulnerable.Check Version:
ssh admin@device_ip 'cat /etc/version' or check web interface system infoVerify Fix Applied:
Verify firmware version >6.x and test that command injection via 'par' parameter no longer works.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to web.cgi with testemail module
- Suspicious commands in system logs
- Multiple failed authentication attempts
Network Indicators:
- POST requests to /web.cgi with 'testemail' and 'par' parameters containing shell metacharacters
- Outbound connections from device to unusual destinations
SIEM Query:
source="device_logs" AND (uri_path="/web.cgi" AND post_data CONTAINS "testemail" AND post_data CONTAINS ["|", ";", "`", "$"] )