CVE-2026-3802: Tenda I3 Firmware Buffer Overflow Flaw

CVE-2026-3802 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda i3 firmware version 1.0.0.6(2204). The vulnerability exists within the formexeCommand function located in the /goform/exeCommand file. By manipulating the cmdinput argument, a remote attacker can trigger a stack-based buffer overflow, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially execute arbitrary code or crash the Tenda i3 device, compromising network infrastructure security.

Affected Products

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

Discovery Timeline

• March 9, 2026 - CVE-2026-3802 published to NVD
• March 9, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3802

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the formexeCommand function, which processes user-supplied input through the cmdinput parameter without proper bounds checking.

When a crafted request is sent to the /goform/exeCommand endpoint, the function fails to validate the length of the input data before copying it to a stack-allocated buffer. This allows an attacker to overwrite adjacent memory on the stack, including return addresses and saved registers. Due to the network-accessible nature of this endpoint, exploitation can be performed remotely by authenticated attackers.

Root Cause

The root cause of this vulnerability is insufficient input validation in the formexeCommand function. The function accepts the cmdinput argument without verifying that its length does not exceed the allocated buffer size. This classic buffer overflow pattern allows stack memory corruption when oversized input is provided, a common issue in embedded device firmware where memory-safe programming practices may not be consistently applied.

Attack Vector

The attack is network-based and can be executed remotely. An authenticated attacker sends a malicious HTTP request to the /goform/exeCommand endpoint with an oversized cmdinput parameter. The vulnerable function copies this input to a fixed-size stack buffer, causing a stack-based buffer overflow. Successful exploitation could enable the attacker to:

• Execute arbitrary code with device privileges
• Crash the device causing denial of service
• Gain persistent access to the network device
• Pivot to attack other devices on the network

A proof-of-concept demonstrating this vulnerability has been publicly disclosed. Technical details can be found in the GitHub Buffer Overflow PoC repository.

Detection Methods for CVE-2026-3802

Indicators of Compromise

• Unusual HTTP POST requests to /goform/exeCommand with abnormally large cmdinput parameters
• Device crashes or unexpected reboots following web management interface access
• Anomalous outbound network connections from the Tenda i3 device
• Modified firmware or configuration files on the device

Detection Strategies

• Monitor web server logs for requests to /goform/exeCommand containing oversized payloads
• Implement network intrusion detection rules to identify buffer overflow exploitation patterns targeting Tenda devices
• Deploy web application firewall rules to block requests with excessively long cmdinput values
• Enable logging on network segments containing Tenda i3 devices and review for suspicious activity

Monitoring Recommendations

• Implement network segmentation to isolate IoT and network infrastructure devices
• Configure SIEM alerts for repeated failed authentication attempts followed by successful access to device management interfaces
• Monitor for firmware integrity changes using file integrity monitoring where applicable
• Review access logs for the Tenda i3 web management interface regularly

How to Mitigate CVE-2026-3802

Immediate Actions Required

• Restrict network access to the Tenda i3 web management interface using firewall rules or access control lists
• Disable remote management access if not required for operations
• Place vulnerable devices behind a VPN or jump host to limit exposure
• Monitor vendor announcements 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. Additional vulnerability tracking information is available through VulDB #349769.

Workarounds

• Implement strict access control lists (ACLs) to limit access to the /goform/exeCommand endpoint
• Use a reverse proxy or web application firewall to filter and validate input length before it reaches the device
• Segment vulnerable Tenda i3 devices onto isolated network VLANs with restricted communication paths
• Consider device replacement if the vendor does not provide a timely security patch

# Example ACL configuration to restrict access to device management
# Adjust IP ranges and interface names as appropriate for your environment
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP