CVE-2026-2907: Tenda HG9 Buffer Overflow Vulnerability

CVE-2026-2907 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda HG9 router firmware version 300001138. This vulnerability exists in the GPON Configuration Endpoint, specifically within the file /boaform/formgponConf. The flaw can be triggered through manipulation of the fmgpon_loid and fmgpon_loid_password arguments, allowing attackers to overflow the stack buffer and potentially execute arbitrary code on the affected device.

The vulnerability is remotely exploitable, making it particularly dangerous for devices exposed to the internet or untrusted networks. According to reports, exploit code has been made publicly available, increasing the risk of active exploitation.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to gain control over Tenda HG9 routers, potentially leading to complete device compromise, network access, and further lateral movement within target environments.

Affected Products

• Tenda HG9 Firmware version 300001138
• Tenda HG9 Hardware

Discovery Timeline

• 2026-02-22 - CVE-2026-2907 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2907

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The GPON Configuration Endpoint at /boaform/formgponConf fails to properly validate the length of input data supplied through the fmgpon_loid and fmgpon_loid_password parameters before copying them to stack-allocated buffers.

When an attacker supplies overly long input strings to these parameters, the data overflows the allocated stack buffer space, corrupting adjacent memory regions including saved return addresses and other critical stack data. This memory corruption can be leveraged to hijack program execution flow.

The network-accessible nature of this endpoint combined with the lack of authentication requirements makes this vulnerability particularly severe for exposed devices.

Root Cause

The root cause of this vulnerability lies in the improper handling of user-supplied input within the GPON configuration handler. The firmware fails to implement adequate bounds checking on the fmgpon_loid and fmgpon_loid_password input parameters before copying data to fixed-size stack buffers. This allows attackers to supply input exceeding the buffer capacity, resulting in stack memory corruption.

Attack Vector

The attack can be executed remotely over the network by sending crafted HTTP requests to the vulnerable /boaform/formgponConf endpoint. An attacker with low-level privileges can send malicious values in the fmgpon_loid or fmgpon_loid_password parameters that exceed expected buffer sizes.

The exploitation involves:

1. Identifying a target Tenda HG9 device with firmware version 300001138
2. Crafting an HTTP request to /boaform/formgponConf with oversized parameter values
3. Overwriting the return address on the stack with attacker-controlled values
4. Redirecting execution to shellcode or ROP gadgets to achieve code execution

The vulnerability can be exploited without user interaction once the attacker has network access to the device. For detailed technical information, refer to the GitHub Issue Discussion and VulDB Entry #347216.

Detection Methods for CVE-2026-2907

Indicators of Compromise

• Unusual HTTP POST requests targeting /boaform/formgponConf with abnormally large parameter values
• Unexpected device reboots or crashes indicating memory corruption attempts
• Suspicious network traffic patterns from the router to unknown external destinations
• Modified firmware or configuration files on the affected device

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests containing oversized fmgpon_loid or fmgpon_loid_password parameters
• Implement network intrusion detection rules to identify buffer overflow exploitation patterns targeting Tenda devices
• Review web server logs for repeated requests to /boaform/formgponConf with anomalous payload sizes
• Deploy SentinelOne Singularity to detect and block exploitation attempts at the endpoint level

Monitoring Recommendations

• Enable logging on network firewalls to capture all traffic destined for router management interfaces
• Implement network segmentation to isolate IoT devices and routers from critical network segments
• Configure alerts for any unauthorized access attempts to the device's administrative interface
• Regularly audit connected devices for signs of compromise or unauthorized configuration changes

How to Mitigate CVE-2026-2907

Immediate Actions Required

• Restrict network access to the Tenda HG9 management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Place the device behind a firewall and block external access to port 80/443
• Monitor for any suspicious activity targeting the device until a patch is available

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 firmware updates and apply patches as soon as they become available.

Until a patch is released, implementing network-level mitigations and access restrictions is strongly recommended. Consider replacing vulnerable devices with alternatives from vendors with better security track records if patching is not timely.

Workarounds

• Configure firewall rules to block all untrusted access to the /boaform/formgponConf endpoint
• Implement network access control lists (ACLs) to restrict management interface access to specific administrator IP addresses
• Consider deploying a reverse proxy with input validation to filter malicious requests
• If the GPON configuration feature is not needed, disable access to the endpoint entirely through firewall rules

# Example iptables rules to restrict access to router management
# Replace 192.168.1.100 with your management workstation IP
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP