CVE-2026-2138: Tenda TX9 Firmware Buffer Overflow Flaw

CVE-2026-2138 Overview

A buffer overflow vulnerability has been identified in Tenda TX9 routers running firmware versions up to 22.03.02.10_multi. The vulnerability exists in the sub_42D03C function within the /goform/SetStaticRouteCfg endpoint, where improper handling of the list argument allows attackers to trigger a buffer overflow condition. This vulnerability can be exploited remotely over the network by authenticated attackers, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers with low-level privileges can exploit this buffer overflow to compromise the confidentiality, integrity, and availability of affected Tenda TX9 routers, potentially gaining full control of the device.

Affected Products

• Tenda TX9 Firmware versions up to 22.03.02.10_multi
• Tenda TX9 Hardware devices

Discovery Timeline

• February 8, 2026 - CVE-2026-2138 published to NVD
• February 10, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2138

Vulnerability Analysis

This vulnerability is classified as a Buffer Overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the firmware's web management interface, specifically within the sub_42D03C function that processes static route configuration requests.

When the /goform/SetStaticRouteCfg endpoint receives a request containing a maliciously crafted list parameter, the function fails to properly validate the length of the input data before copying it into a fixed-size buffer. This allows an attacker to write data beyond the allocated buffer boundaries, potentially corrupting adjacent memory regions.

The vulnerability requires network access and low-level authentication to exploit. A successful attack can result in complete compromise of the router's confidentiality, integrity, and availability, while the impact remains contained to the vulnerable device itself without affecting other connected systems.

Root Cause

The root cause of this vulnerability is insufficient input validation in the sub_42D03C function when processing the list argument in static route configuration requests. The firmware does not implement proper bounds checking before memory operations, allowing oversized input to overflow the designated buffer space. This is a common vulnerability pattern in embedded device firmware where memory safety mechanisms are often limited due to resource constraints.

Attack Vector

The attack vector is network-based, targeting the router's web management interface accessible on the local network. An attacker with valid credentials (low privilege level required) can send a specially crafted HTTP POST request to the /goform/SetStaticRouteCfg endpoint with a malicious list parameter. The exploit has been publicly documented, making it accessible for potential attackers to weaponize.

The attack flow involves:

1. Establishing network connectivity to the target Tenda TX9 router
2. Authenticating with valid credentials (standard user level sufficient)
3. Sending a crafted request to the vulnerable endpoint with an oversized list parameter
4. The buffer overflow corrupts memory, potentially allowing code execution or causing a device crash

Technical details and proof-of-concept information are available in the GitHub IoT Vulnerability Document.

Detection Methods for CVE-2026-2138

Indicators of Compromise

• Unexpected router reboots or instability when accessing the web management interface
• Anomalous HTTP POST requests to /goform/SetStaticRouteCfg with unusually large list parameter values
• Suspicious network traffic patterns indicating exploitation attempts against the router management interface
• Modified router configurations or unexpected static route entries

Detection Strategies

• Monitor network traffic for HTTP requests to /goform/SetStaticRouteCfg endpoints on Tenda devices with abnormally large payloads
• Implement intrusion detection rules to flag potential buffer overflow attempts targeting router management interfaces
• Review router logs for unusual authentication patterns followed by configuration change attempts
• Deploy network segmentation to isolate IoT devices and enable better visibility into management traffic

Monitoring Recommendations

• Enable logging on network firewalls to capture traffic to and from router management interfaces
• Implement network-based anomaly detection for IoT device traffic patterns
• Regularly audit Tenda device firmware versions to identify vulnerable installations
• Consider using SentinelOne Singularity for network visibility to detect exploitation attempts against IoT infrastructure

How to Mitigate CVE-2026-2138

Immediate Actions Required

• Restrict network access to the router's web management interface using firewall rules
• Disable remote management features if not required for operations
• Implement network segmentation to isolate the affected router from critical network assets
• Monitor for firmware updates from Tenda and apply them as soon as available

Patch Information

As of the last update on February 10, 2026, no official patch information has been published by Tenda. Organizations should monitor the Tenda Official Website for security advisories and firmware updates. Additional vulnerability details are available through VulDB #344773 Details.

Workarounds

• Limit access to the router management interface to trusted IP addresses only using access control lists
• Change default credentials and implement strong authentication for router administration
• Disable the web management interface entirely if alternative management methods are available (CLI, console)
• Place the router behind a separate firewall that can inspect and filter malicious requests to the management interface

# Example network isolation using iptables (on upstream firewall)
# Block external access to router management interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow management only from trusted admin workstation
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT