CVE-2023-37929
📋 TL;DR
A buffer overflow vulnerability in the CGI program of Zyxel VMG3625-T50B firmware allows authenticated remote attackers to cause denial of service (DoS) by sending crafted HTTP requests. This affects users of VMG3625-T50B devices running vulnerable firmware versions. Attackers need authentication credentials to exploit this vulnerability.
💻 Affected Systems
- Zyxel VMG3625-T50B
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device crash requiring physical reboot, potential for remote code execution if buffer overflow can be controlled precisely
Likely Case
Temporary denial of service causing device reboot and network disruption
If Mitigated
Minimal impact with proper authentication controls and network segmentation
🎯 Exploit Status
Requires authentication credentials and specific HTTP request crafting
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor advisory for latest patched version
Restart Required: Yes
Instructions:
1. Access device web interface 2. Navigate to firmware update section 3. Download latest firmware from Zyxel support portal 4. Upload and apply firmware update 5. Reboot device
🔧 Temporary Workarounds
Restrict Management Interface Access
allLimit access to device management interface to trusted IP addresses only
Change Default Credentials
allEnsure strong, unique credentials are used for device authentication
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable devices
- Monitor for suspicious HTTP requests to CGI endpoints
🔍 How to Verify
Check if Vulnerable:
Check firmware version in device web interface under System InformationCheck Version:
Check via web interface: System > Status > Firmware VersionVerify Fix Applied:
Verify firmware version matches or exceeds patched version from vendor advisory📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts
- Unusual HTTP requests to CGI endpoints
- Device reboot logs
Network Indicators:
- HTTP POST requests with unusually long parameters to CGI endpoints
- Traffic spikes to management interface
SIEM Query:
source="firewall" AND (url="*.cgi" OR url="*.cgi?*") AND (bytes_out>10000 OR status=500)🔗 References
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-buffer-overflow-vulnerabilities-in-some-5g-nr-4g-lte-cpe-dsl-ethernet-cpe-fiber-ont-wifi-extender-and-home-router-devices-05-21-2024
- https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-buffer-overflow-vulnerabilities-in-some-5g-nr-4g-lte-cpe-dsl-ethernet-cpe-fiber-ont-wifi-extender-and-home-router-devices-05-21-2024
