FIREWALL ZERO-DAY: Critical Zyxel Flaw (CVE-2022-30525) Allows Unauthenticated OS Command Injection and Full Network RCE

 

 

By CyberDudeBivash • September 30, 2025, 09:14 AM IST • Critical Threat Advisory

 

A critical unauthenticated command injection vulnerability in Zyxel firewalls, tracked as **CVE-2022-30525**, is being actively and widely exploited, allowing threat actors to achieve full remote code execution on the network's most critical security device. This flaw allows an attacker to send a single, malicious web request to a vulnerable firewall and gain complete `root` access. A compromised firewall is the ultimate nightmare scenario: the gatekeeper is now the intruder. Attackers are leveraging this access to deploy botnet malware, steal data, and pivot into internal networks to launch ransomware attacks. If your organization is using a vulnerable Zyxel firewall with an exposed management interface, you must act now, as you are not just a potential target—you are actively being scanned for.

 

Disclosure: This is a technical threat report for network administrators, SOC teams, and IT leaders. It contains our full suite of affiliate links to best-in-class solutions for a holistic security posture. Your support helps fund our independent research.

 

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  Threat Report: Table of Contents  

   
1. Chapter 1: Threat Analysis - The Unauthenticated Command Injection
   
2. Chapter 2: The Kill Chain - From Firewall to Botnet
   
3. Chapter 3: The Defender's Playbook - A Guide for Network Admins
   
4. Chapter 4: The Strategic Response - The Folly of Exposed Management Interfaces
   
5. Chapter 5: Extended FAQ on Firewall Hardening
 

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Chapter 1: Threat Analysis - The Unauthenticated Command Injection

The core of CVE-2022-30525 is a command injection vulnerability in a CGI script associated with the firewall's Zero Touch Provisioning (ZTP) feature. This script is exposed via the web management interface and, critically, does not require authentication to access.

The Technical Mechanism

An attacker can send a specifically crafted HTTP POST request to the `/ztp/cgi-bin/ztp.cgi` endpoint. Within the body of this request, the attacker can inject OS-level commands into a JSON object parameter. The script fails to sanitize this input and passes it directly to a system command, which is then executed on the underlying Linux-based OS of the firewall. While the command initially runs as a low-privileged user (`nobody`), the attacker can easily execute a second command to escalate privileges to `root`, gaining complete control over the device.

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Chapter 2: The Kill Chain - From Firewall to Botnet

Threat actors, particularly botnet operators, have automated this attack for maximum speed and scale.

   
1. **Scanning:** Automated scanners and botnets are constantly scouring the internet for Zyxel firewalls with their web management interface (ports 80, 443, etc.) exposed to the WAN.
   
2. **Exploitation:** The moment a vulnerable device is found, the scanner sends the exploit payload. The most common payload is a command that uses `wget` or `curl` to download a malicious shell script from an attacker's server.
   
3. **Persistence & Foothold:** The downloaded script is executed, which establishes a reverse shell back to the attacker's command-and-control (C2) server. This gives the attacker interactive `root` access. The script then often installs malware, such as a Mirai or Muhstik botnet client, for long-term persistence.
   
4. **Defense Evasion & Network Pivot:** The attacker modifies firewall rules to allow their C2 traffic, disables logging, and begins to scan the internal network behind the firewall to find other vulnerable targets.
   
5. **Final Objective:** The compromised firewall is added to a botnet for use in large-scale DDoS attacks. In more targeted attacks, initial access brokers use this foothold to sell access to ransomware gangs, who then proceed to compromise the entire internal network.

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Chapter 3: The Defender's Playbook - A Guide for Network Admins

A two-pronged approach of immediate patching and aggressive hardening is required.

For Corporate SOCs and Network Administrators

   
1. APPLY PATCHED FIRMWARE:** This is the highest priority. Refer to the Zyxel security advisory (Zyxel-SA-2022-0028) and upgrade your device to the specified patched firmware version immediately. This is the only way to fix the flaw.
   
2. DISABLE WAN MANAGEMENT ACCESS:** This is an absolutely critical hardening step. The web management interface of your firewall should never be exposed to the internet. Log in to your firewall and ensure that HTTP/HTTPS management from the WAN zone is disabled. Management should only be done from a secure, internal network.
   
3. HUNT FOR COMPROMISE (Assume Breach):**        
              
   • **Analyze Web Logs:** Review your firewall's access logs for any POST requests to the `/ztp/cgi-bin/ztp.cgi` endpoint. Any such request from an external IP is a definitive indicator of an attack attempt.
              
   • **Check for Unauthorized Accounts/Services:** Review the firewall's configuration for any unfamiliar administrator accounts or services that have been enabled.
              
   • **Monitor Outbound Traffic:** Scrutinize your network traffic logs for any unusual outbound connections originating *from the firewall itself*. A firewall should almost never be initiating outbound connections.
          
      

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Chapter 4: The Strategic Response - The Folly of Exposed Management Interfaces

This incident, like so many before it affecting Cisco, Fortinet, and other network vendors, underscores a dangerous and widespread malpractice: exposing the management interfaces of critical security infrastructure to the public internet. The convenience of being able to manage a firewall from anywhere is massively outweighed by the catastrophic risk it creates.

Every organization must adopt a strict policy that all infrastructure management—for firewalls, switches, servers, and applications—is conducted on isolated, secure, out-of-band management networks. Access to these networks should require a secure connection via a VPN with multi-factor authentication. Reducing your attack surface is one of the most effective security strategies, and closing off public access to your management planes is the biggest and most important step you can take.

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Chapter 5: Extended FAQ on Firewall Hardening

Q: We changed the default management port from 443 to a random high port number. Does this protect us?
A: No, this provides a negligible level of security. Attackers are not just checking port 443; their mass scanners check all 65,535 ports on every IP address for common services. This "security through obscurity" will not stop a determined or automated attacker. The only effective protection is to block access from the WAN zone entirely using the firewall's own rules, and to apply the security patch.The best defense against this type of malware is a modern EDR solution. See our Ultimate Guide to Choosing the Best EDR to learn more.

   

       

About the Author

       

CyberDudeBivash is a cybersecurity strategist and researcher with over 15 years of experience in network security, threat intelligence, and infrastructure hardening. He provides strategic advisory services to CISOs and boards across the APAC region. [Last Updated: September 30, 2025]

   

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