CVE-2026-4043: Tenda i12 Buffer Overflow Vulnerability

CVE-2026-4043 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda i12 router running firmware version 1.0.0.6(2204). The vulnerability exists in the formwrlSSIDget function within the /goform/wifiSSIDget endpoint. By manipulating the index argument, an attacker can trigger a buffer overflow condition that corrupts adjacent stack memory, potentially leading to arbitrary code execution or denial of service.

Critical Impact

Remote attackers with low privileges can exploit this vulnerability over the network to potentially gain control of affected Tenda i12 routers, compromising network security and enabling further lateral movement.

Affected Products

• Tenda i12 Router Firmware version 1.0.0.6(2204)

Discovery Timeline

• 2026-03-12 - CVE-2026-4043 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-4043

Vulnerability Analysis

This vulnerability affects the web management interface of the Tenda i12 router, specifically within the formwrlSSIDget function responsible for handling WiFi SSID configuration requests. The function fails to properly validate the length of the index argument before copying it to a fixed-size stack buffer. When an attacker supplies an oversized value for this parameter, the data overflows the allocated buffer space and overwrites adjacent memory on the stack, including potentially critical control data such as return addresses and saved frame pointers.

The exploitation of this vulnerability can allow attackers to achieve remote code execution on the affected device. Given the embedded nature of router firmware and typically limited security controls, successful exploitation could result in complete device compromise, enabling attackers to intercept network traffic, modify DNS settings, or use the compromised router as a pivot point for attacks against other network resources.

Root Cause

The root cause of this vulnerability is improper bounds checking in the formwrlSSIDget function when processing the index parameter from HTTP requests to /goform/wifiSSIDget. The function allocates a fixed-size buffer on the stack but does not validate that user-supplied input fits within the allocated space before performing memory copy operations. This is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Attack Vector

The vulnerability is exploitable remotely over the network. An authenticated attacker with low-level privileges can send a specially crafted HTTP request to the /goform/wifiSSIDget endpoint with an oversized index parameter. The malicious request does not require user interaction to exploit.

The attack flow proceeds as follows: the attacker crafts an HTTP request targeting the vulnerable endpoint, includes an index parameter with a value exceeding the expected buffer size, the formwrlSSIDget function processes the request without proper bounds validation, and the overflow corrupts stack memory potentially allowing code execution.

For detailed technical analysis and proof-of-concept information, refer to the GitHub Issue Discussion and VulDB Entry #350655.

Detection Methods for CVE-2026-4043

Indicators of Compromise

• Unexpected HTTP requests to /goform/wifiSSIDget with abnormally large index parameter values
• Router crashes or unexpected reboots following web management interface access
• Anomalous outbound connections from the router to unknown external IP addresses
• Modified router configuration settings without administrator action

Detection Strategies

• Monitor HTTP traffic to router management interfaces for requests to /goform/wifiSSIDget with oversized parameters
• Implement network intrusion detection rules to flag requests with excessively long query strings targeting Tenda router endpoints
• Deploy SentinelOne Singularity for IoT to detect exploitation attempts and anomalous router behavior
• Review router logs for authentication failures followed by successful access from the same source

Monitoring Recommendations

• Enable logging on network firewalls for traffic destined to router management interfaces
• Implement alerting for any access to router administration pages from untrusted network segments
• Conduct periodic firmware integrity checks on network infrastructure devices
• Monitor for unusual network traffic patterns that may indicate a compromised router being used for further attacks

How to Mitigate CVE-2026-4043

Immediate Actions Required

• Restrict access to the router management interface to trusted IP addresses only
• Disable remote management access from WAN interfaces if not required
• Place router management interfaces on an isolated VLAN accessible only to network administrators
• Monitor for exploitation attempts using network intrusion detection systems

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Corporate Website for firmware updates addressing this security issue. Additional vulnerability details are tracked at VulDB #350655 and VulDB Submission #769464.

Workarounds

• Implement firewall rules to block external access to the router management interface on port 80/443
• Use a VPN to access router management functions instead of exposing the interface directly
• Configure strong, unique administrative credentials to limit the impact of low-privilege access requirements
• Consider replacing affected devices with alternatives from vendors with better security update practices if no patch is forthcoming

# Example: Firewall rule to restrict management access (iptables)
# Allow management access 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 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP