CVE-2026-3801: Tenda I3 Firmware Buffer Overflow Flaw

CVE-2026-3801 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda i3 firmware version 1.0.0.6(2204). The vulnerability exists in the formSetAutoPing function located in the /goform/setAutoPing endpoint. Remote attackers can exploit this vulnerability by manipulating the ping1 or ping2 arguments to trigger a buffer overflow condition, potentially leading to remote code execution or denial of service on affected devices.

Critical Impact

This network-accessible buffer overflow vulnerability in Tenda i3 routers can be exploited remotely by authenticated attackers to compromise device integrity, confidentiality, and availability. Proof-of-concept exploits have been publicly disclosed.

Affected Products

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

Discovery Timeline

• 2026-03-09 - CVE-2026-3801 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3801

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formSetAutoPing function in Tenda i3 firmware fails to properly validate the length of user-supplied input passed through the ping1 and ping2 parameters. When an attacker submits overly long strings to these parameters via the /goform/setAutoPing web interface endpoint, the function copies this data into a fixed-size stack buffer without adequate bounds checking. This allows an attacker to overwrite adjacent stack memory, including return addresses and saved registers.

The vulnerability is remotely exploitable over the network and requires low-privilege authentication. The attack complexity is low, meaning no special conditions or circumstances are required for exploitation beyond network access to the device's web management interface.

Root Cause

The root cause is improper input validation in the formSetAutoPing function. The firmware developers did not implement proper length checks on the ping1 and ping2 input arguments before copying them into stack-allocated buffers. This is a common vulnerability pattern in embedded device firmware where memory-unsafe C functions are used without proper boundary validation.

Attack Vector

The attack vector is network-based, targeting the device's web management interface at /goform/setAutoPing. An authenticated attacker can craft malicious HTTP requests containing oversized ping1 or ping2 parameter values. When processed by the vulnerable formSetAutoPing function, these oversized inputs overflow the stack buffer, potentially allowing the attacker to:

1. Hijack program execution flow by overwriting return addresses
2. Execute arbitrary code in the context of the web server process
3. Cause denial of service through application crash

The vulnerability has been publicly documented with proof-of-concept exploits available on GitHub, demonstrating both the ping1 and ping2 overflow vectors. Technical details can be found in the ping1 buffer overflow PoC and ping2 buffer overflow PoC repositories.

Detection Methods for CVE-2026-3801

Indicators of Compromise

• Abnormally large HTTP POST requests targeting /goform/setAutoPing endpoint
• Unexpected device reboots or web interface crashes
• Modified device configuration or firmware behavior
• Unusual outbound network connections from the router
• Authentication bypass attempts or credential manipulation

Detection Strategies

• Monitor HTTP traffic for POST requests to /goform/setAutoPing with unusually long ping1 or ping2 parameters
• Implement network intrusion detection rules to flag buffer overflow patterns in web traffic to Tenda devices
• Deploy SentinelOne Singularity to detect and respond to exploitation attempts targeting embedded devices
• Review web server logs on network management systems for anomalous request patterns

Monitoring Recommendations

• Enable verbose logging on network security appliances monitoring traffic to IoT devices
• Implement network segmentation to isolate vulnerable Tenda devices from critical network segments
• Deploy application-layer firewalls capable of inspecting HTTP traffic for oversized parameters
• Establish baseline network behavior for Tenda i3 devices to detect anomalous activity

How to Mitigate CVE-2026-3801

Immediate Actions Required

• Restrict network access to the Tenda i3 web management interface to trusted IP addresses only
• Place affected devices behind a firewall with strict access control rules
• Disable remote management if not required for operations
• Monitor for firmware updates from Tenda addressing this vulnerability
• Consider replacing affected devices if no patch becomes available

Patch Information

No official patch from Tenda has been confirmed at the time of publication. Users should monitor the Tenda Official Website for security updates. Additional vulnerability details are available through VulDB #349768.

Workarounds

• Implement network access control lists (ACLs) to restrict access to the /goform/setAutoPing endpoint
• Use a VPN or secure tunnel for remote management instead of direct internet exposure
• Deploy a web application firewall (WAF) to filter malicious requests before they reach the device
• Consider network segmentation to isolate IoT devices from sensitive network resources

# Example iptables rule to restrict access to Tenda management interface
# Replace 192.168.1.0/24 with your trusted management network
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP