CVE-2026-3799: Tenda I3 Firmware Buffer Overflow Flaw

CVE-2026-3799 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda i3 firmware version 1.0.0.6(2204). The vulnerability exists within the formSetCfm function located in the /goform/setcfm endpoint. By manipulating the funcpara1 argument, an attacker can trigger a stack-based buffer overflow condition. This vulnerability is remotely exploitable over the network, and proof-of-concept exploit code has been publicly disclosed.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow to potentially achieve remote code execution on vulnerable Tenda i3 devices, compromising network infrastructure integrity and confidentiality.

Affected Products

• Tenda i3 Firmware version 1.0.0.6(2204)
• Tenda i3 Hardware devices running vulnerable firmware

Discovery Timeline

• 2026-03-09 - CVE-2026-3799 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3799

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the formSetCfm function which handles form submissions at the /goform/setcfm web endpoint on vulnerable Tenda i3 devices.

When processing the funcpara1 parameter, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer. This lack of bounds checking allows an attacker to supply an overly long value that exceeds the allocated buffer space, causing adjacent stack memory to be overwritten.

The network-accessible nature of this vulnerability means that any authenticated attacker with network access to the device's web management interface can potentially exploit this flaw. The exploitation can lead to complete compromise of the device, affecting confidentiality, integrity, and availability of the system.

Root Cause

The root cause of this vulnerability is insufficient input validation in the formSetCfm function. The code fails to check the length of the funcpara1 argument before copying it into a stack-allocated buffer. This classic buffer overflow pattern occurs when functions like strcpy() or similar unsafe string operations are used without proper length verification, allowing user-controlled data to overflow the destination buffer and corrupt adjacent stack memory.

Attack Vector

The attack can be executed remotely over the network by an authenticated attacker. The exploitation path involves:

1. Gaining authenticated access to the Tenda i3 web management interface
2. Sending a crafted HTTP request to /goform/setcfm with an oversized funcpara1 parameter
3. The malicious input overflows the stack buffer, potentially overwriting the return address
4. When the function returns, execution flow can be redirected to attacker-controlled code

The vulnerability is accessible via the web management interface, making any device with an exposed administrative panel potentially vulnerable. A proof-of-concept demonstrating this attack has been published in a GitHub PoC Repository.

Detection Methods for CVE-2026-3799

Indicators of Compromise

• Unusual HTTP POST requests to /goform/setcfm containing abnormally long funcpara1 values
• Device crashes, reboots, or unexpected behavior following web interface access
• Presence of suspicious payloads in web server logs targeting the /goform/setcfm endpoint
• Anomalous network connections originating from the Tenda i3 device after exploitation

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting /goform/setcfm
• Deploy web application firewall (WAF) rules to inspect and block requests with funcpara1 values exceeding expected lengths
• Monitor device logs for repeated authentication attempts followed by crashes or service restarts
• Use vulnerability scanning tools to identify Tenda i3 devices running firmware version 1.0.0.6(2204)

Monitoring Recommendations

• Enable detailed logging on all Tenda i3 devices and centralize logs for analysis
• Implement network segmentation to isolate IoT and network infrastructure devices from general user traffic
• Set up alerts for any traffic patterns matching known exploitation techniques for this vulnerability
• Regularly audit network inventory to track all Tenda devices and their firmware versions

How to Mitigate CVE-2026-3799

Immediate Actions Required

• Restrict network access to the Tenda i3 web management interface to trusted administrative IP addresses only
• Place vulnerable devices behind a firewall and disable public access to management interfaces
• Monitor for firmware updates from Tenda and apply patches as soon as they become available
• Consider temporarily disabling the web management interface if not required for operations

Patch Information

At the time of publication, no official patch has been announced by Tenda. Organizations should monitor the Tenda Official Website for security advisories and firmware updates addressing this vulnerability. Additional technical details and vulnerability tracking information can be found at VulDB #349766.

Workarounds

• Implement strict access control lists (ACLs) to limit administrative access to the device
• Deploy network-level filtering to block requests with abnormally large parameter values
• Use a reverse proxy with input validation capabilities in front of the device's web interface
• Consider replacing affected devices with alternatives if patches are not released in a timely manner

# Example iptables rule to restrict management interface access
# Allow only trusted admin network to access the device
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP