CVE-2026-2905: Tenda HG9 Buffer Overflow Vulnerability

CVE-2026-2905 Overview

A stack-based buffer overflow vulnerability was identified in Tenda HG9 router firmware version 300001138. This vulnerability affects the /boaform/formWlanSetup endpoint within the Wireless Configuration component. Remote attackers can exploit this flaw by manipulating the ssid argument, potentially leading to arbitrary code execution or denial of service on vulnerable devices.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow vulnerability over the network to compromise affected Tenda HG9 routers, potentially gaining full control of the device or causing service disruption.

Affected Products

• Tenda HG9 Firmware version 300001138
• Tenda HG9 Hardware

Discovery Timeline

• 2026-02-22 - CVE-2026-2905 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2905

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the Wireless Configuration endpoint handler that processes SSID configuration requests. When the ssid parameter is submitted to the /boaform/formWlanSetup endpoint, the application fails to properly validate the length of the input before copying it to a stack-allocated buffer.

The attack can be initiated remotely over the network and requires low privileges to execute. No user interaction is required for exploitation, making this vulnerability particularly dangerous in exposed network environments. The public availability of exploit information increases the risk of active exploitation.

Root Cause

The root cause of CVE-2026-2905 is improper bounds checking in the function responsible for handling the ssid parameter within the /boaform/formWlanSetup endpoint. The firmware fails to validate that user-supplied input does not exceed the allocated buffer size on the stack. When an attacker provides an oversized SSID value, the excess data overwrites adjacent memory on the stack, potentially including return addresses and saved registers.

Attack Vector

The vulnerability is exploitable remotely via HTTP requests to the Wireless Configuration endpoint. An authenticated attacker with low-level access to the router's web interface can craft a malicious request containing an oversized ssid parameter. The attack does not require user interaction and can be automated.

The exploitation technique involves sending a specially crafted HTTP POST request to /boaform/formWlanSetup with a malformed ssid value designed to overflow the stack buffer. By carefully controlling the overflow data, attackers can potentially overwrite the return address and redirect execution to attacker-controlled code, achieving remote code execution on the device.

Technical details and exploit information are publicly available in the GitHub Issue Discussion referenced in the vulnerability disclosure.

Detection Methods for CVE-2026-2905

Indicators of Compromise

• Unusual HTTP POST requests to /boaform/formWlanSetup containing abnormally long ssid parameter values
• Router crashes or unexpected reboots following wireless configuration changes
• Unexplained modifications to router wireless settings or administrative credentials
• Network traffic anomalies originating from the router to unknown external destinations

Detection Strategies

• Implement web application firewall rules to detect and block HTTP requests with oversized ssid parameters targeting /boaform/formWlanSetup
• Monitor router logs for repeated access attempts to the Wireless Configuration endpoint from unusual source IP addresses
• Deploy network intrusion detection signatures to identify buffer overflow exploit payloads in HTTP traffic
• Configure alerting for router service restarts or crash events that may indicate exploitation attempts

Monitoring Recommendations

• Enable logging on all HTTP requests to router administrative interfaces and review for anomalous patterns
• Monitor router firmware integrity using file integrity monitoring where supported
• Implement network segmentation to isolate IoT devices and routers from critical network segments
• Deploy SentinelOne Singularity for network visibility to detect lateral movement following potential router compromise

How to Mitigate CVE-2026-2905

Immediate Actions Required

• Restrict access to the router's administrative web interface to trusted IP addresses only
• Disable remote management if not required for operations
• Implement network access controls to prevent unauthorized access to the /boaform/formWlanSetup endpoint
• Monitor for firmware updates from Tenda and apply patches as soon as they become available

Patch Information

At the time of publication, no official patch from Tenda has been confirmed for this vulnerability. Organizations should monitor the Tenda Security Information page for official security advisories and firmware updates. Additional technical details are available through the VulDB Resource #347214.

Workarounds

• Place the Tenda HG9 router behind a firewall that blocks external access to the web management interface
• Use network ACLs to restrict which internal hosts can access router administrative functions
• Consider replacing the affected device with an alternative router that receives regular security updates
• If wireless configuration is required, perform changes via physical access rather than the web interface when possible

# Example: Restrict access to router management interface using iptables
# Apply these rules on an upstream firewall or gateway device
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP
iptables -A INPUT -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT