CVE-2024-40890
📋 TL;DR
This is a post-authentication command injection vulnerability in Zyxel VMG4325-B10A DSL CPE devices that allows authenticated attackers to execute arbitrary operating system commands via crafted HTTP POST requests. It affects users of the legacy Zyxel VMG4325-B10A firmware version 1.00(AAFR.4)C0_20170615. Attackers must first authenticate to the device before exploiting this vulnerability.
💻 Affected Systems
- Zyxel VMG4325-B10A DSL CPE
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to install persistent backdoors, intercept all network traffic, pivot to internal networks, or brick the device.
Likely Case
Attacker gains full control of the router to modify configurations, steal credentials, or use as a foothold for further attacks.
If Mitigated
Limited impact if strong authentication controls prevent unauthorized access and network segmentation limits lateral movement.
🎯 Exploit Status
Exploitation requires authentication first, but attackers may leverage default credentials or credential stuffing. CISA has added this to their Known Exploited Vulnerabilities catalog.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: No firmware update available - device is end-of-life
Restart Required: No
Instructions:
1. Replace affected device with supported hardware. 2. If replacement is not possible, implement strict network controls and workarounds. 3. Change all default credentials immediately.
🔧 Temporary Workarounds
Network Segmentation
allIsolate affected devices from critical networks and limit management interface access
Access Control Restrictions
allRestrict management interface access to specific IP addresses only
🧯 If You Can't Patch
- Replace device with supported hardware immediately
- Implement strict network segmentation and firewall rules to limit device access
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or SSH: System Information > Firmware VersionCheck Version:
Check web interface at System Information or use SSH/Telnet to check firmware versionVerify Fix Applied:
Verify device has been replaced with supported hardware or isolated from network📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP POST requests to CGI endpoints
- Multiple failed authentication attempts followed by successful login
- Unexpected command execution in system logs
Network Indicators:
- HTTP POST requests with shell metacharacters in parameters
- Outbound connections from router to suspicious IPs
- Unusual traffic patterns from router management interface
SIEM Query:
source="router_logs" AND (http_method="POST" AND uri="*.cgi" AND (param CONTAINS "|" OR param CONTAINS ";" OR param CONTAINS "`"))