CVE-2026-3803: Tenda I3 Firmware Buffer Overflow Flaw

CVE-2026-3803 Overview

A stack-based buffer overflow vulnerability was identified in Tenda i3 firmware version 1.0.0.6(2204). This vulnerability affects the function formWifiMacFilterGet located in the file /goform/WifiMacFilterGet. The manipulation of the index argument leads to a stack-based buffer overflow condition. This vulnerability can be initiated remotely over the network by an authenticated attacker, potentially leading to device compromise, arbitrary code execution, or denial of service.

Critical Impact
Remote attackers with low privileges can exploit this stack-based buffer overflow to achieve high impact on confidentiality, integrity, and availability of the affected Tenda i3 device.

Affected Products

Tenda i3 Firmware version 1.0.0.6(2204)
Tenda i3 Hardware Device

Discovery Timeline

2026-03-09 - CVE-2026-3803 published to NVD
2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3803

Vulnerability Analysis

This vulnerability is classified as CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer. The vulnerable function formWifiMacFilterGet in the Tenda i3 firmware does not properly validate the length of the index argument before copying it to a stack-allocated buffer. When an attacker supplies an oversized value for the index parameter, the function writes beyond the intended memory boundaries, corrupting adjacent stack memory.

The exploitation of this buffer overflow can allow an attacker to overwrite critical stack data including return addresses and saved frame pointers. This can lead to arbitrary code execution with the privileges of the web server process running on the device, complete device takeover, or crash the service causing denial of service.

The attack can be executed remotely over the network with low privileges required, making it accessible to authenticated users on the local network or potentially from the internet if the device's management interface is exposed.

Root Cause

The root cause of this vulnerability is improper input validation in the formWifiMacFilterGet function. The code fails to check the length of user-supplied data in the index parameter before copying it into a fixed-size stack buffer. This is a classic buffer overflow pattern where boundary checking is absent, allowing attackers to supply data that exceeds the allocated buffer size and overwrite adjacent memory on the stack.

Attack Vector

The attack is network-based and targets the web management interface of the Tenda i3 device. An attacker sends a crafted HTTP request to the /goform/WifiMacFilterGet endpoint with a maliciously crafted index parameter containing data that exceeds the expected buffer size. When the vulnerable function processes this request, the oversized input overflows the stack buffer, potentially allowing the attacker to hijack the control flow of the program.

The vulnerability is publicly documented with a proof-of-concept available in the GitHub PoC Repository. Additional technical intelligence is available through VulDB Entry #349770.

Detection Methods for CVE-2026-3803

Indicators of Compromise

Anomalous HTTP requests to /goform/WifiMacFilterGet with unusually large index parameter values
Unexpected device reboots or crashes of the web management service
Evidence of unauthorized configuration changes or firmware modifications
Network traffic patterns indicating exploitation attempts against the device's web interface

Detection Strategies

Implement network intrusion detection rules to identify HTTP requests to /goform/WifiMacFilterGet with oversized parameters
Monitor web server logs on the Tenda i3 device for suspicious requests containing abnormally long input values
Deploy application-layer firewall rules to filter requests with excessive parameter lengths to the vulnerable endpoint
Use behavioral analysis to detect memory corruption indicators such as unexpected process crashes or restarts

Monitoring Recommendations

Continuously monitor network traffic to and from Tenda i3 devices for exploitation attempts
Set up alerts for HTTP requests to vulnerable endpoints with parameters exceeding normal operational values
Implement logging of all administrative access to the device's web interface
Review device stability logs for unexpected crashes that may indicate exploitation attempts

How to Mitigate CVE-2026-3803

Immediate Actions Required

Restrict network access to the Tenda i3 management interface to trusted IP addresses only
Disable remote management access if not required for operations
Place the Tenda i3 device behind a network firewall with strict access controls
Monitor the Tenda Official Website for security advisories and firmware updates

Patch Information

As of the last modification date of this CVE (2026-03-09), no official patch has been released by Tenda. Organizations should monitor vendor communications and apply any security updates immediately when they become available. Consider replacing vulnerable devices if patches are not forthcoming in a reasonable timeframe.

Workarounds

Implement network segmentation to isolate affected Tenda i3 devices from untrusted networks
Use a web application firewall (WAF) to filter requests with oversized parameters to the /goform/WifiMacFilterGet endpoint
Disable the web management interface entirely and use alternative management methods if available
Consider deploying VPN access for device management to reduce attack surface exposure

bash

# Example firewall rule to restrict access to device management interface
# Block external access to the Tenda i3 management port (adjust interface and IP as needed)
iptables -A INPUT -i eth0 -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP