CVE-2026-4042: Tenda i12 Buffer Overflow Vulnerability

CVE-2026-4042 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda i12 routers running firmware version 1.0.0.6(2204). The vulnerability exists in the formWifiMacFilterGet function within the /goform/WifiMacFilterGet endpoint. An attacker can exploit this flaw by manipulating the index argument, leading to a stack-based buffer overflow condition. This vulnerability can be exploited remotely over the network, and proof-of-concept exploit code has been publicly disclosed.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to potentially achieve high impact on confidentiality, integrity, and availability of affected Tenda i12 routers, potentially leading to device compromise or denial of service.

Affected Products

• Tenda i12 Firmware Version 1.0.0.6(2204)

Discovery Timeline

• March 12, 2026 - CVE-2026-4042 published to NVD
• March 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-4042

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The affected function formWifiMacFilterGet fails to properly validate the bounds of the index argument before processing user-supplied input. When an attacker provides a specially crafted value for this parameter, the function writes data beyond the allocated stack buffer, corrupting adjacent memory regions.

The network-accessible nature of this vulnerability is particularly concerning for IoT devices like routers, which are often deployed at network perimeters. Successful exploitation could allow attackers to execute arbitrary code with the privileges of the affected process, potentially gaining full control over the router.

Root Cause

The root cause of this vulnerability stems from improper bounds checking in the formWifiMacFilterGet function when handling the index parameter. The function allocates a fixed-size buffer on the stack but does not validate that user-supplied input fits within this buffer before copying data. This classic memory safety issue allows attackers to overflow the buffer and overwrite critical stack data, including return addresses and saved frame pointers.

Attack Vector

The attack is initiated remotely over the network by sending a malicious HTTP request to the /goform/WifiMacFilterGet endpoint. An attacker with low-level authentication can craft a request containing an oversized or malicious index parameter value. When the vulnerable function processes this input without proper validation, the stack-based buffer overflow occurs.

The vulnerability can be exploited without user interaction, making it suitable for automated attack scenarios. Attackers could leverage this flaw to:

• Achieve remote code execution on the router
• Cause denial of service by crashing the device
• Pivot to attack other devices on the internal network

Technical details and proof-of-concept information are available in the GitHub Issue Report.

Detection Methods for CVE-2026-4042

Indicators of Compromise

• Unusual HTTP requests to /goform/WifiMacFilterGet with abnormally large index parameter values
• Unexpected router crashes or reboots indicating potential exploitation attempts
• Anomalous outbound traffic from the router suggesting compromise
• Modified router configuration or unexpected administrative changes

Detection Strategies

• Deploy network intrusion detection rules to monitor for malformed HTTP requests targeting /goform/WifiMacFilterGet
• Implement deep packet inspection to identify oversized parameters in requests to Tenda router web interfaces
• Monitor router logs for repeated crashes or service restarts that may indicate exploitation attempts
• Use SentinelOne Singularity platform to detect anomalous behavior patterns on network endpoints

Monitoring Recommendations

• Enable logging on all Tenda i12 devices and forward logs to a centralized SIEM for analysis
• Configure alerts for any access attempts to the vulnerable endpoint from untrusted networks
• Implement network segmentation to limit exposure of management interfaces
• Regularly audit router configurations for unauthorized changes

How to Mitigate CVE-2026-4042

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Place affected Tenda i12 devices behind a firewall that filters access to /goform/ endpoints
• Consider disabling the web management interface if not required for operations
• 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. Organizations should monitor the Tenda Official Website for security updates and firmware releases addressing CVE-2026-4042.

Additional vulnerability tracking information is available through:

• VulDB Entry #350654
• VulDB CTI ID #350654

Workarounds

• Implement network ACLs to restrict access to the router management interface from untrusted networks
• Deploy a Web Application Firewall (WAF) to filter malicious requests targeting the vulnerable endpoint
• Consider replacing affected devices with alternative hardware if no patch becomes available
• Use VPN-only access for remote management to reduce attack surface

# Example iptables rules to restrict access to router management
# Apply these rules on a firewall protecting the Tenda i12 device

# Block external access to goform endpoints
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -m string --string "/goform/" --algo bm -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -m string --string "/goform/" --algo bm -j DROP

# Allow management access only from trusted admin subnet
iptables -A FORWARD -s <TRUSTED_SUBNET> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP