CVE-2020-27158
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary code on Western Digital My Cloud NAS devices via the cgi_api.php file, potentially leading to full system compromise. It affects users of these devices with firmware versions prior to 5.04.114, enabling privilege escalation from unauthenticated or low-privileged access.
💻 Affected Systems
- Western Digital My Cloud NAS devices
📦 What is this software?
My Cloud Firmware by Westerndigital
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains full control of the NAS device, accesses or deletes all stored data, installs malware, and uses it as a pivot point to attack other internal network systems.
Likely Case
Attackers exploit the vulnerability to steal sensitive files, encrypt data for ransomware, or use the device for botnet activities like DDoS attacks.
If Mitigated
With proper network segmentation and access controls, impact is limited to the NAS device itself, preventing lateral movement and reducing data exposure.
🎯 Exploit Status
Exploitation involves sending crafted requests to cgi_api.php; public proof-of-concept code exists, making it easy for attackers to weaponize.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.04.114
Vendor Advisory: https://www.westerndigital.com/support/productsecurity/wdc-20007-my-cloud-firmware-version-5-04-114
Restart Required: Yes
Instructions:
1. Log into the My Cloud web interface. 2. Navigate to Settings > Firmware Update. 3. Check for updates and install version 5.04.114 or later. 4. Reboot the device after installation.
🔧 Temporary Workarounds
Block External Access
linuxPrevent remote exploitation by blocking internet access to the NAS device using firewall rules.
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
Disable Web Interface
linuxTemporarily disable the web interface to reduce attack surface, though this limits management capabilities.
systemctl stop apache2
systemctl disable apache2
🧯 If You Can't Patch
- Isolate the NAS device on a separate VLAN with strict access controls to limit exposure to trusted internal networks only.
- Implement network monitoring and intrusion detection to alert on suspicious activity targeting cgi_api.php or unusual outbound connections.
🔍 How to Verify
Check if Vulnerable:
Check the firmware version via the web interface at Settings > Firmware Update; if version is below 5.04.114, the device is vulnerable.Check Version:
curl -s http://<NAS_IP>/cgi-bin/device.cgi?cmd=get_fw_versionVerify Fix Applied:
After updating, confirm the firmware version shows 5.04.114 or higher in the same settings menu.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /cgi-bin/cgi_api.php with suspicious parameters
- Failed login attempts followed by successful command execution logs
Network Indicators:
- Spikes in traffic to port 80/443 on the NAS device from unknown IPs
- Outbound connections from the NAS to malicious domains or IPs post-exploit
SIEM Query:
source="nas_logs" AND (uri="/cgi-bin/cgi_api.php" AND method="POST" AND status=200) | stats count by src_ip🔗 References
- https://www.comparitech.com/blog/information-security/security-vulnerabilities-80000-devices-update-now/
- https://www.westerndigital.com/support/productsecurity
- https://www.westerndigital.com/support/productsecurity/wdc-20007-my-cloud-firmware-version-5-04-114
- https://www.comparitech.com/blog/information-security/security-vulnerabilities-80000-devices-update-now/
- https://www.westerndigital.com/support/productsecurity
- https://www.westerndigital.com/support/productsecurity/wdc-20007-my-cloud-firmware-version-5-04-114
