CVE-2026-3975: Tenda W3 Buffer Overflow Vulnerability

CVE-2026-3975 Overview

A critical stack-based buffer overflow vulnerability has been discovered in Tenda W3 router firmware version 1.0.0.3(2204). The vulnerability exists in the formWifiMacFilterGet function within the /goform/WifiMacFilterGet endpoint of the POST Parameter Handler component. By manipulating the wl_radio argument, an attacker can trigger a stack-based buffer overflow condition. This vulnerability is remotely exploitable, and a proof-of-concept exploit has been publicly released, increasing the risk of active exploitation in the wild.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially achieve arbitrary code execution on affected Tenda W3 routers, leading to complete device compromise and network infiltration.

Affected Products

• Tenda W3 Firmware 1.0.0.3(2204)
• Tenda W3 Router devices running vulnerable firmware versions

Discovery Timeline

• 2026-03-12 - CVE-2026-3975 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-3975

Vulnerability Analysis

This vulnerability is classified as a memory boundary violation (CWE-119) that specifically manifests as a stack-based buffer overflow. The affected function formWifiMacFilterGet processes incoming HTTP POST requests without properly validating the length of user-supplied input in the wl_radio parameter. When an attacker sends a specially crafted POST request with an oversized wl_radio value, the function copies this data onto the stack without adequate bounds checking, causing a buffer overflow condition.

The network-accessible nature of this vulnerability significantly increases its risk profile, as attackers can exploit it remotely without requiring physical access to the device. The low attack complexity combined with the potential for high impact on confidentiality, integrity, and availability makes this a serious security concern for affected router deployments. The public availability of exploit code further elevates the threat level, as it lowers the barrier for malicious actors to weaponize this vulnerability.

Root Cause

The root cause of CVE-2026-3975 lies in improper input validation within the formWifiMacFilterGet function. The function fails to enforce proper boundary checks when processing the wl_radio parameter from POST requests. When user-controlled data exceeds the allocated buffer size on the stack, it overwrites adjacent memory regions, potentially including the return address and other critical stack data. This classic buffer overflow pattern allows attackers to hijack program execution flow.

Attack Vector

The attack is conducted remotely over the network by sending malicious HTTP POST requests to the /goform/WifiMacFilterGet endpoint on the vulnerable Tenda W3 router. An authenticated attacker can craft a POST request containing an oversized wl_radio parameter value designed to overflow the stack buffer. The attack requires low privilege access to the router's web interface but does not require user interaction.

The exploitation mechanism involves:

1. Identifying a target Tenda W3 router running firmware version 1.0.0.3(2204)
2. Sending a crafted POST request to /goform/WifiMacFilterGet with a malicious wl_radio parameter
3. The oversized input overflows the stack buffer in formWifiMacFilterGet
4. Overwritten return addresses redirect execution to attacker-controlled code

For detailed technical analysis and proof-of-concept code, refer to the GitHub PoC for Buffer Overflow.

Detection Methods for CVE-2026-3975

Indicators of Compromise

• Unusual HTTP POST requests to /goform/WifiMacFilterGet with abnormally large wl_radio parameter values
• Router crash events or unexpected reboots indicating potential exploitation attempts
• Suspicious outbound network connections from the router to unknown IP addresses
• Unauthorized configuration changes or new administrative accounts on the router

Detection Strategies

• Implement network traffic analysis to monitor for POST requests to /goform/WifiMacFilterGet with payload sizes exceeding normal operational parameters
• Deploy intrusion detection system (IDS) rules to flag requests containing the vulnerable endpoint and oversized parameters
• Monitor router system logs for crash reports or memory corruption events associated with the web interface

Monitoring Recommendations

• Enable verbose logging on network perimeter devices to capture traffic destined for Tenda router management interfaces
• Implement SIEM correlation rules to detect multiple failed or anomalous requests to router administration endpoints
• Conduct regular firmware version audits to identify devices running vulnerable Tenda W3 firmware 1.0.0.3(2204)

How to Mitigate CVE-2026-3975

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not absolutely required for operations
• Implement network segmentation to isolate affected Tenda W3 devices from critical network resources
• Monitor Tenda's official channels for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Administrators should monitor the Tenda Official Website for security updates and firmware releases. Additional vulnerability details are available through VulDB #350410.

Workarounds

• Configure firewall rules to block external access to port 80/443 on affected Tenda W3 routers
• Implement access control lists (ACLs) to restrict management interface access to specific administrator workstations
• Consider replacing affected devices with alternative router solutions until a patch becomes available
• Deploy a Web Application Firewall (WAF) in front of the router management interface to filter malicious POST requests

# Example iptables rules to restrict router management access
# Allow management only from trusted admin subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
# Block all other management access
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP