CVE-2026-5338: Tenda G103 Command Injection Vulnerability

CVE-2026-5338 Overview

A command injection vulnerability has been identified in Tenda G103 router firmware version 1.0.0.5. The vulnerability exists within the action_set_system_settings function located in the system.lua file of the Setting Handler component. Attackers can exploit this flaw by manipulating the lanIp argument, allowing arbitrary command execution on the affected device. This vulnerability can be exploited remotely over the network.

Critical Impact

Remote attackers with privileged access can inject and execute arbitrary system commands on Tenda G103 routers, potentially leading to full device compromise, network infiltration, and persistent backdoor installation.

Affected Products

• Tenda G103 firmware version 1.0.0.5
• Tenda G103 Setting Handler component (system.lua)
• Tenda G103 action_set_system_settings function

Discovery Timeline

• April 2, 2026 - CVE-2026-5338 published to NVD
• April 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5338

Vulnerability Analysis

This command injection vulnerability (CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component) affects the network configuration functionality of Tenda G103 routers. The vulnerability resides in the action_set_system_settings function within the system.lua file, which is part of the device's Setting Handler component.

When processing LAN IP address configuration requests, the function fails to properly sanitize user-supplied input in the lanIp parameter before incorporating it into system commands. This allows an authenticated attacker with high privileges to inject malicious commands that will be executed with the permissions of the web server process, typically running as root on embedded devices.

The exploit has been publicly disclosed, increasing the risk of widespread exploitation against unpatched devices.

Root Cause

The root cause of this vulnerability is insufficient input validation and sanitization in the action_set_system_settings function. The lanIp parameter is directly passed to system command execution without proper escaping or validation of special characters. This allows command separators (such as semicolons, pipes, or backticks) to be interpreted by the underlying shell, enabling arbitrary command injection.

Attack Vector

The attack can be performed remotely over the network by an authenticated attacker with administrative privileges. The attacker sends a specially crafted HTTP request to the router's web interface, embedding malicious shell commands within the lanIp parameter value.

The vulnerability requires network access to the device's management interface and administrative credentials. An attacker who has gained access to the router's administrative panel (through credential theft, default credentials, or other means) can leverage this vulnerability to execute arbitrary commands on the underlying operating system.

For technical details about the exploitation mechanism, see the GitHub Repository for Tenda G103 and VulDB Vulnerability #354669.

Detection Methods for CVE-2026-5338

Indicators of Compromise

• Unusual HTTP requests to the router's Setting Handler with malformed or suspicious lanIp parameter values containing shell metacharacters
• Unexpected processes or network connections originating from the Tenda G103 device
• Modified configuration files or unauthorized changes to system settings
• Presence of unauthorized scripts or binaries in the router's filesystem

Detection Strategies

• Monitor HTTP traffic to the router's management interface for requests containing command injection patterns (semicolons, pipes, backticks, $(...) constructs) in the lanIp parameter
• Implement network-based intrusion detection rules targeting the action_set_system_settings endpoint with suspicious payloads
• Review router access logs for authentication anomalies or repeated configuration change attempts

Monitoring Recommendations

• Enable and centralize logging for the Tenda G103 device's web management interface
• Deploy network monitoring to detect unusual outbound connections from IoT devices
• Implement behavioral analysis for the router to identify deviations from normal operation patterns

How to Mitigate CVE-2026-5338

Immediate Actions Required

• Restrict access to the router's management interface to trusted IP addresses only
• Ensure strong, unique administrative credentials are in place and avoid using default passwords
• Place the Tenda G103 management interface behind a firewall or on an isolated management VLAN
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Organizations should monitor the vendor's website and security advisories for firmware updates. In the interim, implementing network-level access controls and monitoring is strongly recommended.

Additional technical details and tracking information can be found at VulDB Submission Page #781131 and VulDB CTI for #354669.

Workarounds

• Disable remote management access to the router if not required for operations
• Implement firewall rules to block external access to the device's web interface on port 80/443
• Use a VPN for remote administration rather than exposing the management interface directly to the network
• Consider replacing vulnerable devices with alternatives that have active security support if patches are not forthcoming

# Example firewall rule to restrict management interface access
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s !192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s !192.168.1.0/24 -j DROP