CVE-2026-3807: Tenda FH1202 Buffer Overflow Vulnerability

CVE-2026-3807 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda FH1202 wireless router firmware version 1.2.0.14(408). The vulnerability exists in the formWrlsafeset function located in the /goform/AdvSetWrlsafeset endpoint. Attackers can exploit this flaw by manipulating the mit_ssid or mit_ssid_index parameters, leading to memory corruption and potentially enabling remote code execution on the affected device.

Critical Impact

Remote attackers with low-level privileges can exploit this buffer overflow vulnerability to execute arbitrary code or cause denial of service on vulnerable Tenda FH1202 routers. The exploit has been publicly disclosed and may be actively used in attacks targeting consumer and small business networks.

Affected Products

• Tenda FH1202 Firmware version 1.2.0.14(408)
• Tenda FH1202 Hardware devices running vulnerable firmware

Discovery Timeline

• 2026-03-09 - CVE-2026-3807 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3807

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formWrlsafeset function fails to properly validate the length of user-supplied input for the mit_ssid and mit_ssid_index parameters before copying them to a fixed-size stack buffer. When an attacker provides an overly long string, the buffer boundaries are exceeded, overwriting adjacent memory on the stack including the return address and other critical control flow data.

The network-accessible nature of this vulnerability allows remote exploitation without requiring physical access to the device. An authenticated attacker with low privileges can craft malicious HTTP requests to the /goform/AdvSetWrlsafeset endpoint, providing specially crafted values that trigger the overflow condition.

Root Cause

The root cause is insufficient bounds checking in the formWrlsafeset function when processing the mit_ssid and mit_ssid_index HTTP parameters. The firmware copies user input directly to a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This is a classic stack-based buffer overflow pattern commonly found in embedded device firmware written in C/C++ without modern memory safety protections.

Attack Vector

The attack is executed remotely over the network by sending crafted HTTP POST requests to the vulnerable endpoint. The attacker must have low-level authentication to the router's web interface, after which they can submit malicious parameter values designed to overflow the stack buffer.

The exploitation flow typically involves:

1. Authenticating to the router's web management interface
2. Sending a crafted POST request to /goform/AdvSetWrlsafeset
3. Including an oversized mit_ssid or mit_ssid_index parameter value
4. Overwriting the return address to redirect execution to attacker-controlled code

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

Detection Methods for CVE-2026-3807

Indicators of Compromise

• Abnormal HTTP POST requests to /goform/AdvSetWrlsafeset with unusually long parameter values
• Router crashes, reboots, or unresponsive behavior following web interface access
• Unexpected network traffic patterns originating from the router
• Modified router configuration or unauthorized administrative access

Detection Strategies

• Monitor HTTP traffic to router management interfaces for requests containing oversized mit_ssid or mit_ssid_index parameters
• Implement intrusion detection rules to flag POST requests to /goform/AdvSetWrlsafeset with parameter lengths exceeding normal thresholds
• Deploy network-based anomaly detection to identify exploitation attempts against IoT devices
• Review router access logs for unusual authentication patterns or repeated requests to wireless configuration endpoints

Monitoring Recommendations

• Segment IoT devices including routers on isolated network VLANs with restricted access
• Enable logging on router management interfaces where supported
• Monitor for firmware integrity changes or unauthorized configuration modifications
• Implement network flow analysis to detect command-and-control traffic from compromised devices

How to Mitigate CVE-2026-3807

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Disable remote management features if not required
• Implement strong authentication credentials for router administration
• Consider network segmentation to isolate vulnerable devices from critical systems
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no vendor patch has been confirmed. Organizations should monitor Tenda's official channels for security updates. Given the public disclosure of this vulnerability and availability of exploitation details, applying patches immediately upon release is strongly recommended.

Workarounds

• Disable the web management interface and use alternative management methods where possible
• Implement firewall rules to restrict access to /goform/AdvSetWrlsafeset and other sensitive endpoints
• Use a VPN or jump host to access router management interfaces rather than exposing them directly
• Consider replacing vulnerable devices with alternatives that receive regular security updates

# Example firewall rule to restrict router management access (adjust IP ranges as needed)
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP