CVE-2026-3808: Tenda FH1202 Buffer Overflow Vulnerability

CVE-2026-3808 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda FH1202 firmware version 1.2.0.14(408). The vulnerability exists in the formWebTypeLibrary function within the /goform/webtypelibrary file. By manipulating the webSiteId argument, an attacker can trigger a stack-based buffer overflow condition. This vulnerability can be exploited remotely by an authenticated attacker, and a public exploit is currently available.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow to potentially execute arbitrary code or cause denial of service on affected Tenda FH1202 routers, compromising network security and device integrity.

Affected Products

• Tenda FH1202 Firmware version 1.2.0.14(408)
• Tenda FH1202 Hardware

Discovery Timeline

• 2026-03-09 - CVE-2026-3808 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3808

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 web management interface of the Tenda FH1202 router, specifically within the formWebTypeLibrary function that processes HTTP requests to the /goform/webtypelibrary endpoint.

The function fails to properly validate the length of user-supplied input in the webSiteId parameter before copying it into a fixed-size stack buffer. When an attacker provides an oversized value for this parameter, the data overflows the allocated buffer space on the stack, potentially overwriting adjacent memory regions including return addresses and saved registers.

Successful exploitation could allow an attacker to corrupt the execution flow of the application, potentially leading to arbitrary code execution with the privileges of the web server process, or causing a denial of service condition through application crash.

Root Cause

The root cause of this vulnerability is insufficient input validation in the formWebTypeLibrary function. The code does not perform adequate bounds checking on the webSiteId parameter before processing it, allowing user-controlled data to exceed the allocated buffer size on the stack. This is a classic example of improper memory safety practices in embedded firmware development, where string handling functions do not enforce length restrictions on input data.

Attack Vector

The attack can be initiated remotely over the network by sending a specially crafted HTTP request to the vulnerable /goform/webtypelibrary endpoint. The attacker must have low-level authentication to access this functionality. The attack does not require user interaction, making it particularly dangerous in scenarios where the router's management interface is exposed to untrusted networks.

An attacker would craft an HTTP POST request containing an oversized webSiteId parameter designed to overflow the stack buffer. The payload could be designed to overwrite the return address on the stack, redirecting program execution to attacker-controlled code or causing the device to crash.

For detailed technical analysis and proof-of-concept information, refer to the GitHub PoC Repository and the VulDB entry #349774.

Detection Methods for CVE-2026-3808

Indicators of Compromise

• Unusual HTTP POST requests to /goform/webtypelibrary with abnormally long webSiteId parameter values
• Router crashes or unexpected reboots that may indicate exploitation attempts
• Anomalous network traffic patterns originating from the router's management interface
• Log entries showing malformed requests to web management endpoints

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting Tenda router management interfaces
• Monitor for repeated connection attempts to the /goform/webtypelibrary endpoint from external sources
• Deploy web application firewall rules to block requests with webSiteId parameters exceeding expected length thresholds
• Analyze network traffic for patterns consistent with buffer overflow exploitation attempts

Monitoring Recommendations

• Enable logging on network perimeter devices to capture all traffic to router management interfaces
• Implement alerting for any access to router administration pages from non-trusted IP addresses
• Regularly review router access logs for suspicious activity patterns
• Consider deploying SentinelOne Singularity for network visibility to detect exploitation attempts and lateral movement following compromise

How to Mitigate CVE-2026-3808

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if not required for operations
• Implement network segmentation to isolate vulnerable devices from untrusted networks
• Monitor for any suspicious activity targeting the affected endpoint

Patch Information

As of the last update on 2026-03-09, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for security updates and firmware releases. Consider replacing affected devices with alternatives from vendors with better security update practices if patches are not forthcoming.

Workarounds

• Disable the web management interface entirely if feasible and manage the device through other means
• Use firewall rules to block external access to port 80/443 on the affected device
• Place the router behind an additional firewall or access control device
• Consider firmware replacement with open-source alternatives if compatible and supported

# Example iptables rules to restrict access to router management interface
# Run on upstream firewall/gateway device

# Block external access to router management port
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP

# Allow only specific management hosts
iptables -I FORWARD -s <ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT