CVE-2026-3974: Tenda W3 Buffer Overflow Vulnerability

CVE-2026-3974 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda W3 router firmware version 1.0.0.3(2204). This vulnerability exists within the formexeCommand function located in the /goform/exeCommand endpoint of the HTTP Handler component. An attacker can exploit this flaw by manipulating the cmdinput argument, leading to a stack-based buffer overflow condition. This vulnerability can be exploited remotely over the network, making it particularly dangerous for exposed devices.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow to potentially execute arbitrary code on vulnerable Tenda W3 routers, compromising the entire network segment.

Affected Products

• Tenda W3 Router Firmware Version 1.0.0.3(2204)

Discovery Timeline

• March 12, 2026 - CVE-2026-3974 published to NVD
• March 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3974

Vulnerability Analysis

This vulnerability affects the formexeCommand function within the Tenda W3 router's HTTP Handler component. The function processes user-supplied input from the cmdinput parameter without proper boundary validation, resulting in a classic stack-based buffer overflow condition (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer).

The vulnerability is accessible via the /goform/exeCommand endpoint, which handles HTTP requests for command execution functionality on the device. When an authenticated attacker sends a specially crafted request with an oversized cmdinput value, the input exceeds the allocated buffer space on the stack, potentially overwriting critical memory structures including return addresses.

Exploitation of this vulnerability could allow an attacker to achieve arbitrary code execution on the affected device with the privileges of the web server process, typically running as root on embedded devices like routers.

Root Cause

The root cause of this vulnerability lies in the insufficient bounds checking within the formexeCommand function when processing the cmdinput parameter. The function fails to validate the length of user-supplied input before copying it to a fixed-size stack buffer. This allows an attacker to supply input that exceeds the buffer's capacity, resulting in stack corruption.

Embedded devices like the Tenda W3 often utilize legacy C code without modern memory safety protections, making them particularly susceptible to buffer overflow vulnerabilities. The lack of stack canaries, ASLR, or other exploit mitigations on these devices further increases the exploitability of such flaws.

Attack Vector

The attack can be performed remotely over the network by an authenticated attacker. The exploitation process involves:

1. The attacker authenticates to the router's web interface (low privilege requirement)
2. A crafted HTTP request is sent to the /goform/exeCommand endpoint
3. The cmdinput parameter contains a payload exceeding the expected buffer size
4. The oversized input overwrites the stack, including the return address
5. Upon function return, execution flow is redirected to attacker-controlled code

The vulnerability is present in the HTTP Handler component, meaning any network-accessible interface to the router's administrative functions could be leveraged for exploitation. A proof-of-concept exploit has been publicly documented in the GitHub PoC Repository.

Detection Methods for CVE-2026-3974

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/exeCommand with unusually large cmdinput parameter values
• Web server crashes or unexpected reboots on Tenda W3 devices
• Anomalous outbound network connections from the router to unknown external IP addresses
• Modifications to router configuration or firmware without administrative action

Detection Strategies

• Monitor network traffic for HTTP requests targeting /goform/exeCommand endpoints on Tenda devices
• Implement intrusion detection rules to flag requests with cmdinput parameters exceeding normal operational lengths
• Deploy network segmentation to isolate IoT and router management interfaces from general network traffic
• Review router access logs for repeated authentication attempts followed by requests to the vulnerable endpoint

Monitoring Recommendations

• Enable verbose logging on Tenda W3 devices if available and regularly export logs to a centralized SIEM
• Monitor for firmware integrity changes using file integrity monitoring solutions where applicable
• Establish baseline network behavior for router devices and alert on deviations
• Implement network-level monitoring for connections originating from router management interfaces

How to Mitigate CVE-2026-3974

Immediate Actions Required

• Restrict network access to the router's administrative interface using firewall rules or ACLs
• Disable remote administration features if not required for business operations
• Ensure strong, unique credentials are configured for router administration
• Consider network segmentation to isolate vulnerable devices from critical assets
• Monitor for firmware updates from Tenda and apply patches when available

Patch Information

At the time of publication, no official patch from Tenda has been confirmed. Organizations should monitor the Tenda Official Website for security advisories and firmware updates addressing CVE-2026-3974. Additional vulnerability details are available through VulDB #350409.

Workarounds

• Implement network access control lists (ACLs) to restrict access to the /goform/exeCommand endpoint
• Place the router behind a firewall that filters traffic to administrative interfaces
• Disable the web-based administration interface if command-line or SNMP management alternatives are available
• Consider replacing affected devices with models that have better security support and update cycles

# Example iptables rule to restrict access to router admin interface
# Replace 192.168.1.1 with your router's IP and 192.168.1.100 with trusted admin workstation
iptables -A INPUT -d 192.168.1.1 -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -d 192.168.1.1 -p tcp --dport 80 -j DROP