Tenda AC7 / AC9 / AC10 Routers goform/setUsbUnload Remote Command Injection Vulnerability (CVE-2018-14558) Analysis and Mitigation Guide

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2018-14558) is a critical OS command injection vulnerability found in the web management interface of Tenda SOHO routers, specifically AC7, AC9, and AC10 models. The root cause lies in the handling of the 'goform/setUsbUnload' API endpoint. The internal 'formsetUsbUnload' function processes user-supplied input parameters and passes them directly to the 'dosystemCmd' function without adequate sanitization or validation, allowing shell metacharacters to be executed by the underlying operating system.

2. Exploitation Mechanics & Attack Scenario

An attacker can exploit this vulnerability by sending a specially crafted HTTP POST request to the 'goform/setUsbUnload' endpoint. By embedding shell metacharacters (such as ';', '&&', '`', or '|') along with malicious commands into the request parameters, the attacker forces the router's web daemon to execute those commands with administrative (root) privileges. Since this endpoint does not require prior authentication, any remote attacker with network access to the web interface can compromise the device.

3. Infrastructure & Business Impact

With a CVSS 3.1 score of 9.8 (Critical) and its inclusion in the CISA Known Exploited Vulnerabilities (KEV) catalog, this vulnerability poses an active threat. Successful exploitation allows attackers to establish persistent access, recruit the device into IoT botnets (e.g., Mirai), perform man-in-the-middle (MitM) attacks, alter DNS settings to redirect users to phishing sites, or use the compromised router as a pivot point to attack internal corporate networks.