Full Report
Zyxel security advisory (AV26-399)
Analysis Summary
# Vulnerability: Command Injection in Zyxel CPE, ONT, and Wireless Devices
## CVE Details
*Note: The specific CVE IDs and CVSS scores are referenced under the aggregate advisory released on April 28, 2026.*
- **CVE ID:** CVE-2026-XXXXX (Multiple vulnerabilities covered under the advisory)
- **CVSS Score:** 8.1 - 9.8 (Estimated range for Critical Command Injections)
- **CWE:** CWE-78 (Improper Neutralization of Special Elements used in an OS Command)
## Affected Systems
- **Products:**
- 4G LTE/5G NR CPE
- DSL/Ethernet CPE
- Fiber ONTs (Optical Network Terminals)
- Wireless Extenders
- **Versions:** Multiple versions across various models. Specific model-by-model firmware requirements are listed in the vendor’s technical library.
- **Configurations:** Devices with management interfaces (Web GUI) accessible via the network.
## Vulnerability Description
The flaws consist of command injection vulnerabilities within the web management interface of various Zyxel networking devices. These vulnerabilities occur due to improper validation of user-supplied input. An attacker can craft malicious requests to the device's management component that include OS commands, which the device then executes with elevated privileges (typically root).
## Exploitation
- **Status:** Not exploited in the wild (at time of advisory release); however, Zyxel devices are frequent targets for Mirai-like botnets once advisories are public.
- **Complexity:** Low
- **Attack Vector:** Network (Remote)
## Impact
- **Confidentiality:** High (Full access to device configuration and traffic)
- **Integrity:** High (Ability to modify firmware, settings, and DNS)
- **Availability:** High (Ability to brick the device or use it in DDoS attacks)
## Remediation
### Patches
Users are urged to identify their specific model and apply the latest firmware update released on or after April 28, 2026.
- **4G LTE/5G NR CPE:** Consult Zyxel support for model-specific firmware.
- **DSL/Ethernet CPE:** Consult Zyxel support for model-specific firmware.
- **Fiber ONTs:** Updates typically delivered through Service Providers; manual updates may be required for retail units.
- **Wireless Extenders:** Check the local management interface for "Check for Updates."
### Workarounds
- **Disable Remote Management:** Ensure the Web GUI is not accessible from the WAN (Internet) side.
- **VLAN Isolation:** Keep management interfaces on a dedicated, restricted management VLAN.
- **ACLs:** Implement Access Control Lists to restrict access to the device's IP address to trusted administrative hosts only.
## Detection
- **Indicators of Compromise:** Unusual outbound traffic on non-standard ports, unexpected reboots, or unauthorized changes to DNS settings.
- **Detection methods:** Monitor system logs for shell metacharacters (e.g., `;`, `|`, `&`, `$()`) within HTTP POST/GET requests directed at the management interface.
## References
- Zyxel Security Advisory: hxxps[://]www[.]zyxel[.]com/global/en/support/security-advisories/zyxel-security-advisory-for-command-injection-vulnerabilities-in-certain-4g-lte-5g-nr-cpe-dsl-ethernet-cpe-fiber-onts-and-wireless-extenders-04-28-2026
- Zyxel Security Center: hxxps[://]www[.]zyxel[.]com/global/en/support/security-advisories
- Canadian Centre for Cyber Security (AV26-399): hxxps[://]www[.]cyber[.]gc[.]ca/en/alerts-advisories/zyxel-security-advisory-av26-399