CVE-2026-4008: Tenda W3 Buffer Overflow Vulnerability

CVE-2026-4008 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda W3 router firmware version 1.0.0.3(2204). The vulnerability exists in the POST Parameter Handler component, specifically within the /goform/wifiSSIDset endpoint. An attacker can exploit this flaw by manipulating the index or GO arguments in crafted HTTP POST requests, leading to a stack-based buffer overflow condition. The vulnerability is remotely exploitable, and proof-of-concept exploit code has been published publicly.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow to potentially achieve arbitrary code execution on vulnerable Tenda W3 routers, compromising network infrastructure and enabling lateral movement within affected environments.

Affected Products

• Tenda W3 Firmware version 1.0.0.3(2204)

Discovery Timeline

• 2026-03-12 - CVE-2026-4008 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-4008

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the web management interface of the Tenda W3 router, where the /goform/wifiSSIDset endpoint fails to properly validate the length of user-supplied input in the index and GO POST parameters.

When processing HTTP POST requests to this endpoint, the firmware copies user-controlled data into a fixed-size stack buffer without adequate bounds checking. If an attacker supplies oversized input values, the data overwrites adjacent stack memory, including the return address. This enables an attacker to hijack program execution flow and potentially execute arbitrary code with the privileges of the web server process.

The vulnerability is exploitable remotely over the network, requiring only low-privilege authentication to the device's web interface. No user interaction is required beyond the initial authentication.

Root Cause

The root cause of this vulnerability is improper input validation in the POST parameter handling code for the /goform/wifiSSIDset form handler. The index and GO parameters are copied into stack-allocated buffers using unsafe string operations that do not enforce proper length restrictions, allowing attackers to overflow the buffer boundaries. This is a classic stack-based buffer overflow caused by insufficient bounds checking on user-controlled input in embedded device firmware.

Attack Vector

The attack vector is network-based, targeting the web management interface of the Tenda W3 router. An attacker with network access to the device and low-level authentication can craft malicious HTTP POST requests to the /goform/wifiSSIDset endpoint with oversized index or GO parameter values.

The exploitation flow involves:

1. Authenticating to the Tenda W3 web management interface
2. Sending a crafted POST request to /goform/wifiSSIDset with an oversized index or GO parameter
3. The malicious payload overflows the stack buffer, overwriting the return address
4. Upon function return, execution is redirected to attacker-controlled memory

Proof-of-concept exploits demonstrating this attack have been published. For technical details, refer to the GitHub PoC for Buffer Overflow and GitHub PoC for Index Buffer Overflow repositories.

Detection Methods for CVE-2026-4008

Indicators of Compromise

• Unusual HTTP POST requests to /goform/wifiSSIDset with abnormally large parameter values
• Unexpected crashes or reboots of Tenda W3 routers
• Anomalous network traffic patterns originating from router management interfaces
• Unauthorized configuration changes on affected devices

Detection Strategies

• Monitor HTTP traffic for POST requests to /goform/wifiSSIDset containing oversized index or GO parameters
• Implement network intrusion detection rules to alert on buffer overflow attack patterns targeting Tenda devices
• Deploy anomaly detection for unexpected router behavior such as crashes, reboots, or performance degradation
• Review web server logs on Tenda devices for malformed or suspicious POST requests

Monitoring Recommendations

• Establish baseline behavior for router management interface access and alert on deviations
• Implement network segmentation to restrict access to router management interfaces from untrusted networks
• Configure logging for all administrative access attempts to Tenda W3 devices
• Use SentinelOne Singularity platform to monitor network endpoints for lateral movement following potential router compromise

How to Mitigate CVE-2026-4008

Immediate Actions Required

• Restrict network access to the Tenda W3 management interface to trusted administrative hosts only
• Implement firewall rules to block external access to port 80/443 on vulnerable devices
• Monitor for any signs of exploitation attempts in network traffic
• Consider temporarily disabling the web management interface if not required for operations

Patch Information

At the time of publication, no official patch information is available from Tenda. Organizations should monitor the Tenda Official Site for firmware updates addressing this vulnerability. Additional vulnerability details are available at VulDB #350531.

Workarounds

• Isolate affected Tenda W3 routers on a separate network segment with restricted access
• Disable remote management features and only allow local administration
• Implement strong access controls and authentication for the router management interface
• Consider replacing vulnerable devices with alternatives that receive regular security updates
• Deploy network-level intrusion prevention systems to block exploit attempts

# Example firewall rule to restrict management interface access
# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP