CVE-2026-2139: Tenda TX9 Firmware Buffer Overflow Flaw

CVE-2026-2139 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 function sub_432580 within the file /goform/fast_setting_wifi_set, which handles WiFi configuration settings. Improper handling of the ssid argument allows an attacker to trigger a buffer overflow condition that can lead to memory corruption and potential remote code execution.

This vulnerability affects consumer-grade networking equipment commonly deployed in home and small office environments. The exploit has been publicly disclosed, increasing the urgency for affected users to take protective measures.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially execute arbitrary code on affected Tenda TX9 routers, compromising network infrastructure and enabling further attacks on connected devices.

Affected Products

• Tenda TX9 Firmware versions up to 22.03.02.10_multi
• Tenda TX9 Hardware devices running vulnerable firmware

Discovery Timeline

• 2026-02-08 - CVE-2026-2139 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-2139

Vulnerability Analysis

The vulnerability resides in the WiFi configuration handling mechanism of the Tenda TX9 router firmware. The affected function sub_432580 processes user-supplied input from the /goform/fast_setting_wifi_set endpoint, which is part of the router's web-based management interface. When processing the ssid parameter, the function fails to properly validate the length of the input data before copying it into a fixed-size buffer.

This buffer overflow vulnerability (classified as CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) allows attackers to overwrite adjacent memory regions. The network-accessible nature of this endpoint means authenticated attackers can exploit this remotely through the router's management interface without requiring physical access to the device.

Root Cause

The root cause of this vulnerability is insufficient input validation in the sub_432580 function. The ssid argument is not properly bounds-checked before being processed, allowing an attacker to supply an oversized value that exceeds the allocated buffer capacity. This lack of boundary enforcement is a common issue in embedded device firmware where memory safety practices may not be rigorously applied due to resource constraints or legacy code.

Attack Vector

The attack can be initiated remotely via the network by sending a specially crafted HTTP POST request to the /goform/fast_setting_wifi_set endpoint on the router's web management interface. The attacker must have network access to the router's management interface and supply a malformed ssid parameter containing data that exceeds expected bounds. This triggers the buffer overflow in the sub_432580 function, potentially allowing the attacker to overwrite critical memory structures such as return addresses or function pointers.

The attack requires low-privilege authentication to the router's web interface but does not require user interaction once access is obtained. Successful exploitation can result in complete compromise of the router's confidentiality, integrity, and availability.

For detailed technical analysis and proof-of-concept information, see the GitHub IoT Vulnerability Documentation.

Detection Methods for CVE-2026-2139

Indicators of Compromise

• Unusual HTTP POST requests to /goform/fast_setting_wifi_set containing abnormally long ssid parameter values
• Router instability, unexpected reboots, or unresponsive web management interface
• Unexpected changes to WiFi SSID configuration or router settings
• Suspicious outbound network traffic from the router to unknown external addresses

Detection Strategies

• Monitor network traffic for HTTP requests to the /goform/fast_setting_wifi_set endpoint with payloads exceeding normal SSID length limits (typically 32 characters)
• Implement network-based intrusion detection rules to identify buffer overflow attack patterns targeting Tenda router endpoints
• Review router access logs for authentication anomalies or repeated configuration change attempts
• Deploy web application firewalls (WAF) to filter requests with oversized parameters to router management interfaces

Monitoring Recommendations

• Enable logging on network segments where Tenda TX9 routers are deployed to capture management interface access attempts
• Configure alerts for any access to router administration interfaces from unexpected source IP addresses
• Periodically verify router firmware versions and configuration integrity against known-good baselines
• Monitor for firmware modifications or unauthorized configuration changes through scheduled audits

How to Mitigate CVE-2026-2139

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote administration features if not required for operations
• Implement network segmentation to isolate vulnerable router devices from untrusted network segments
• Consider deploying affected routers behind a firewall that can filter malicious requests to the /goform/ endpoints

Patch Information

At the time of publication, no official security patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for firmware updates that address CVE-2026-2139. Additional technical details are available through VulDB #344774.

Workarounds

• Change default administrative credentials and enforce strong passwords for router management access
• Bind the management interface to specific trusted IP addresses or MAC addresses where supported
• Disable the web management interface entirely if router configuration changes are not frequently required
• Use network access control lists (ACLs) to limit which hosts can communicate with the router's management ports