CVE-2023-37928
📋 TL;DR
A post-authentication command injection vulnerability in Zyxel NAS devices allows authenticated attackers to execute arbitrary OS commands by sending crafted URLs to the WSGI server. This affects Zyxel NAS326 and NAS542 devices with specific firmware versions. Attackers must first authenticate to the device before exploiting this vulnerability.
💻 Affected Systems
- Zyxel NAS326
- Zyxel NAS542
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the NAS device leading to data theft, ransomware deployment, lateral movement to other network systems, and persistent backdoor installation.
Likely Case
Unauthorized access to sensitive files stored on the NAS, modification or deletion of data, and potential credential harvesting from the compromised device.
If Mitigated
Limited impact due to network segmentation, strong authentication controls, and monitoring that detects unusual command execution patterns.
🎯 Exploit Status
Exploitation requires authentication first, but the command injection itself is straightforward once authenticated. Public proof-of-concept code exists.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to latest firmware versions as specified in Zyxel security advisories
Restart Required: Yes
Instructions:
1. Download latest firmware from Zyxel support portal. 2. Backup NAS data. 3. Log into web interface. 4. Navigate to Maintenance > Firmware Upgrade. 5. Upload firmware file. 6. Wait for reboot and verify version.
🔧 Temporary Workarounds
Network Segmentation
allIsolate NAS devices from internet and restrict access to trusted networks only
Strong Authentication Controls
allImplement multi-factor authentication, strong password policies, and account lockouts
🧯 If You Can't Patch
- Remove NAS web interface from internet exposure immediately
- Implement strict network access controls and monitor for unusual authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check firmware version in NAS web interface under Maintenance > System InformationCheck Version:
Check via web interface or SSH if enabled: cat /etc/versionVerify Fix Applied:
Verify firmware version has been updated to a version not listed in affected versions📡 Detection & Monitoring
Log Indicators:
- Unusual command execution in system logs
- Multiple failed authentication attempts followed by successful login
- Web server logs showing crafted URLs with command injection patterns
Network Indicators:
- Unusual outbound connections from NAS device
- Traffic patterns indicating data exfiltration
- HTTP requests with command injection payloads to WSGI endpoints
SIEM Query:
source="nas-logs" AND (url="*;*" OR url="*|*" OR url="*`*" OR url="*$(*")🔗 References
- https://bugprove.com/knowledge-hub/cve-2023-37927-and-cve-2023-37928-multiple-post-auth-blind-os-command-and-python-code-injection-vulnerabilities-in-zyxel-s-nas-326-devices/
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-authentication-bypass-and-command-injection-vulnerabilities-in-nas-products
- https://bugprove.com/knowledge-hub/cve-2023-37927-and-cve-2023-37928-multiple-post-auth-blind-os-command-and-python-code-injection-vulnerabilities-in-zyxel-s-nas-326-devices/
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-authentication-bypass-and-command-injection-vulnerabilities-in-nas-products
