CVE-2022-43391
📋 TL;DR
A buffer overflow vulnerability in the CGI program of Zyxel NR7101 firmware allows authenticated attackers to cause denial-of-service conditions by sending specially crafted HTTP requests. This affects Zyxel NR7101 devices running firmware versions prior to V1.15(ACCC.3)C0. The vulnerability requires authentication but could disrupt network connectivity for affected devices.
💻 Affected Systems
- Zyxel NR7101
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device crash requiring physical reboot, extended network downtime, and potential for remote code execution if the buffer overflow can be leveraged beyond DoS.
Likely Case
Temporary denial-of-service causing device reboot or service interruption, disrupting network connectivity for connected users.
If Mitigated
Minimal impact with proper network segmentation and access controls limiting authenticated access to vulnerable interfaces.
🎯 Exploit Status
Exploitation requires authenticated access to the web interface. The buffer overflow is in CGI parameter handling.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V1.15(ACCC.3)C0
Restart Required: Yes
Instructions:
1. Download firmware V1.15(ACCC.3)C0 from Zyxel support portal. 2. Log into NR7101 web interface. 3. Navigate to Maintenance > Firmware Upgrade. 4. Upload the firmware file. 5. Wait for upgrade to complete and device to reboot.
🔧 Temporary Workarounds
Restrict Web Interface Access
allLimit access to the NR7101 web management interface to trusted IP addresses only.
Configure firewall rules to restrict access to port 80/443 on NR7101 to specific management IPs
Disable Remote Management
allDisable remote web management if not required, forcing local network access only.
In NR7101 web interface: System > Remote Management > Disable
🧯 If You Can't Patch
- Implement strict network segmentation to isolate NR7101 devices from untrusted networks
- Change default credentials and implement strong authentication policies for device management
🔍 How to Verify
Check if Vulnerable:
Check firmware version in NR7101 web interface under System > System Info. If version is earlier than V1.15(ACCC.3)C0, device is vulnerable.Check Version:
curl -k https://[device-ip]/cgi-bin/luci/; show version in web interfaceVerify Fix Applied:
After patching, verify firmware version shows V1.15(ACCC.3)C0 or later in System > System Info.📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by large HTTP requests to CGI endpoints
- Device reboot logs without normal shutdown sequence
Network Indicators:
- Unusually large HTTP POST requests to /cgi-bin/ endpoints
- Sudden loss of connectivity to NR7101 device
SIEM Query:
source="nr7101-logs" AND (uri_path="/cgi-bin/*" AND content_length>10000) OR event_type="device_reboot"🔗 References
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-command-injection-and-buffer-overflow-vulnerabilities-of-cpe-fiber-onts-and-wifi-extenders
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-command-injection-and-buffer-overflow-vulnerabilities-of-cpe-fiber-onts-and-wifi-extenders
