CVE-2014-3919
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in Netgear CG3100 cable modems that allows attackers to inject malicious scripts into web pages. When exploited, it can enable information theft from users who visit compromised pages. Only Netgear CG3100 devices running firmware versions before 3.9.2421.13.mp3 V0027 are affected.
💻 Affected Systems
- Netgear CG3100
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal administrator credentials, hijack user sessions, redirect users to malicious sites, or perform actions on behalf of authenticated users, potentially leading to complete device compromise.
Likely Case
Attackers would steal session cookies or authentication tokens to gain unauthorized access to the modem's administrative interface, then modify network settings or intercept traffic.
If Mitigated
With proper network segmentation and access controls, the impact would be limited to the local network segment containing the vulnerable device.
🎯 Exploit Status
The vulnerability requires user interaction (visiting a malicious page) but doesn't require authentication. XSS exploits are commonly weaponized in phishing campaigns.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.9.2421.13.mp3 V0027 or later
Vendor Advisory: http://softage.be/netgear/
Restart Required: Yes
Instructions:
1. Log into the Netgear CG3100 web interface. 2. Navigate to the firmware update section. 3. Download firmware version 3.9.2421.13.mp3 V0027 or later from Netgear's support site. 4. Upload and apply the firmware update. 5. Reboot the device after the update completes.
🔧 Temporary Workarounds
Restrict Web Interface Access
allLimit access to the modem's web management interface to trusted IP addresses only
Configure firewall rules to restrict access to port 80/443 on the modem to specific management IPs
Disable Remote Management
allTurn off remote management features if not required
In web interface: Advanced > Remote Management > Disable
🧯 If You Can't Patch
- Isolate the Netgear CG3100 on a separate VLAN with strict access controls
- Implement a web application firewall (WAF) in front of the device to filter malicious scripts
🔍 How to Verify
Check if Vulnerable:
Check firmware version in web interface: Login > Router Status > Firmware Version. If version is earlier than 3.9.2421.13.mp3 V0027, device is vulnerable.Check Version:
curl -s http://[router-ip]/router_status.html | grep -i firmwareVerify Fix Applied:
After updating, verify firmware version shows 3.9.2421.13.mp3 V0027 or later in the Router Status page.📡 Detection & Monitoring
Log Indicators:
- Unusual JavaScript payloads in web server logs
- Multiple failed login attempts followed by successful login from different IP
- Unexpected changes to modem configuration
Network Indicators:
- HTTP requests containing script tags or JavaScript payloads to the modem's IP
- Traffic redirection to unexpected domains
SIEM Query:
source="netgear_logs" AND (http_uri="*<script*" OR http_user_agent="*<script*" OR http_referer="*javascript:*")