CVE-2025-11730
📋 TL;DR
This CVE describes a post-authentication command injection vulnerability in Zyxel firewall devices. An authenticated attacker with administrator privileges can execute arbitrary operating system commands by injecting malicious strings into the Dynamic DNS configuration CLI command. This affects multiple Zyxel firewall series running specific firmware versions.
💻 Affected Systems
- Zyxel ATP series
- USG FLEX series
- USG FLEX 50(W) series
- USG20(W)-VPN series
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to install persistent backdoors, exfiltrate configuration data, pivot to internal networks, or render the firewall inoperable.
Likely Case
Attacker with legitimate admin credentials (compromised or malicious insider) gains full control of the firewall to intercept traffic, modify rules, or use as a foothold for lateral movement.
If Mitigated
Limited impact due to strong access controls, multi-factor authentication, and network segmentation preventing lateral movement even if device is compromised.
🎯 Exploit Status
Exploitation requires valid administrator credentials. The vulnerability is in a CLI command, making exploitation straightforward once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V5.42 or later
Restart Required: Yes
Instructions:
1. Download firmware V5.42 or later from Zyxel support portal. 2. Backup current configuration. 3. Upload new firmware via web interface or CLI. 4. Reboot device. 5. Verify firmware version after reboot.
🔧 Temporary Workarounds
Restrict CLI Access
allLimit CLI access to trusted administrative accounts only and implement strong authentication controls.
Disable Unnecessary DDNS Features
allIf Dynamic DNS functionality is not required, disable it to remove the attack vector.
🧯 If You Can't Patch
- Implement strict access controls and multi-factor authentication for all administrative accounts
- Segment firewall management interfaces from general user networks and monitor for suspicious CLI activity
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface (System > Maintenance > Firmware) or CLI command 'show version'Check Version:
show versionVerify Fix Applied:
Confirm firmware version is V5.42 or later using same methods as checking vulnerability📡 Detection & Monitoring
Log Indicators:
- Unusual CLI command execution patterns
- Multiple failed authentication attempts followed by successful login
- DDNS configuration changes from unexpected sources
Network Indicators:
- Unexpected outbound connections from firewall management interface
- Anomalous traffic patterns through firewall
SIEM Query:
source="zyxel-firewall" AND (event_type="cli_command" AND command="*ddns*" AND user!="expected_admin")