CVE-2025-11847
📋 TL;DR
An authenticated attacker with administrator privileges can cause a denial-of-service condition on affected Zyxel devices by sending a specially crafted HTTP request that triggers a null pointer dereference in the IP settings CGI program. This affects Zyxel VMG3625-T50B and WX3100-T0 devices running vulnerable firmware versions.
💻 Affected Systems
- Zyxel VMG3625-T50B
- Zyxel WX3100-T0
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Device becomes completely unresponsive, requiring physical reboot or factory reset to restore functionality, disrupting network services for all users.
Likely Case
Temporary service interruption affecting the web interface and potentially network routing functions until device automatically reboots or is manually restarted.
If Mitigated
Minimal impact with proper network segmentation and monitoring, as exploitation requires admin credentials and only affects specific device models.
🎯 Exploit Status
Exploitation requires authenticated admin access to the web interface. The vulnerability is in a specific CGI program handling IP settings.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Zyxel advisory for specific patched versions
Restart Required: Yes
Instructions:
1. Log into Zyxel support portal
2. Download latest firmware for your device model
3. Access device web interface
4. Navigate to Maintenance > Firmware Upgrade
5. Upload and apply firmware update
6. Reboot device after update completes
🔧 Temporary Workarounds
Restrict admin interface access
allLimit access to the web administration interface to trusted IP addresses only
Configure firewall rules to restrict access to device management IP/port
Disable remote admin access
allDisable web administration from WAN/Internet interfaces
In device settings: disable 'Remote Management' or similar feature
🧯 If You Can't Patch
- Implement strict network segmentation to isolate affected devices from untrusted networks
- Monitor for unusual HTTP requests to the admin interface and implement rate limiting
🔍 How to Verify
Check if Vulnerable:
Check firmware version in web interface under Maintenance > System Info or via CLI command 'show version'Check Version:
show version (CLI) or check web interface System Info pageVerify Fix Applied:
Verify firmware version is newer than affected versions listed in advisory📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by successful login and HTTP requests to /cgi-bin/ip_settings.cgi
- Device reboot events without scheduled maintenance
Network Indicators:
- HTTP POST requests to /cgi-bin/ip_settings.cgi with malformed parameters
- Sudden loss of connectivity to device management interface
SIEM Query:
source="zyxel_device" AND (uri_path="/cgi-bin/ip_settings.cgi" OR event_type="device_reboot")