CVE-2018-21156
📋 TL;DR
This vulnerability allows an authenticated attacker to execute a buffer overflow attack on certain NETGEAR devices. It affects multiple NETGEAR routers, gateways, and extenders running outdated firmware versions. Successful exploitation could allow arbitrary code execution on the affected device.
💻 Affected Systems
- NETGEAR D6220
- D6400
- D7000v2
- D8500
- DGN2200v4
- DGN2200Bv4
- EX3700
- EX3800
- EX6000
- EX6100
- EX6120
- EX6130
- EX6150
- EX6200
- EX7000
- R6250
- R6300v2
- R6400
- R6400v2
- R6700
- R6900
- R6900P
- R7000
- R7000P
- R7300DST
- R7900
- R7900P
- R8000
- R8000P
- R8300
- R8500
- WN2500RPv2
- WNDR3400v3
- WNR3500Lv2
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to execute arbitrary code, modify device configuration, intercept network traffic, or use device as pivot point for further attacks.
Likely Case
Device instability, crashes, or limited code execution leading to configuration changes or network disruption.
If Mitigated
Minimal impact if proper network segmentation and access controls prevent authenticated attackers from reaching vulnerable interfaces.
🎯 Exploit Status
Requires authenticated access to the device. Buffer overflow (CWE-120) typically requires specific knowledge of memory layout and exploitation techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions specified in CVE description (e.g., D6220 1.0.0.38 or later)
Vendor Advisory: https://kb.netgear.com/000059474/Security-Advisory-for-Post-Authentication-Buffer-Overflow-on-Some-Gateways-Routers-and-Extenders-PSV-2017-2460
Restart Required: Yes
Instructions:
1. Identify your NETGEAR device model. 2. Visit NETGEAR support website. 3. Download latest firmware for your model. 4. Log into router admin interface. 5. Navigate to firmware update section. 6. Upload and install new firmware. 7. Device will restart automatically.
🔧 Temporary Workarounds
Restrict administrative access
allLimit administrative interface access to trusted IP addresses only
Configure firewall rules to restrict access to router admin interface (typically ports 80/443)
Use strong authentication
allImplement complex passwords and consider disabling remote administration
Change default admin password to strong unique password
Disable remote administration if not needed
🧯 If You Can't Patch
- Segment network to isolate vulnerable devices from critical systems
- Implement strict access controls and monitor for suspicious authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check current firmware version in router admin interface under Advanced > Administration > Router Update or similar sectionCheck Version:
Log into router web interface and navigate to firmware/version information pageVerify Fix Applied:
Verify firmware version matches or exceeds patched versions listed in CVE description📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by successful login
- Unusual administrative access patterns
- Device crash/reboot logs
Network Indicators:
- Unusual traffic to/from router administrative ports
- Suspicious payloads in HTTP requests to router interface
SIEM Query:
source="router_logs" AND (event_type="authentication" AND result="success") AND user!="expected_admin" OR event_type="device_reboot"