CVE-2026-2909: Tenda HG9 Buffer Overflow Vulnerability

CVE-2026-2909 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda HG9 router firmware version 300001138. This vulnerability exists in the /boaform/formPing endpoint, which handles diagnostic ping operations. By manipulating the pingAddr argument with malicious input, an authenticated remote attacker can trigger a stack-based buffer overflow condition, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

This vulnerability allows remote attackers with low privileges to potentially achieve full device compromise through stack-based buffer overflow exploitation, affecting the confidentiality, integrity, and availability of the router.

Affected Products

• Tenda HG9 Firmware version 300001138
• Tenda HG9 Router Hardware

Discovery Timeline

• 2026-02-22 - CVE-2026-2909 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2909

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The affected component is the Diagnostic Ping Endpoint located at /boaform/formPing in the Tenda HG9 router's web management interface.

The vulnerability stems from insufficient input validation when processing the pingAddr parameter. When a user submits a ping diagnostic request through the web interface, the router processes the target address without properly checking the length of the input. This allows an attacker to provide an overly long string that exceeds the allocated buffer on the stack, resulting in a classic stack-based buffer overflow condition.

Network-based exploitation is possible, meaning attackers with network access to the device's management interface can potentially trigger this vulnerability remotely. The exploit has been publicly disclosed, increasing the risk of active exploitation in the wild.

Root Cause

The root cause is improper bounds checking in the handling of the pingAddr parameter within the /boaform/formPing endpoint. The firmware fails to validate the length of user-supplied input before copying it into a fixed-size stack buffer. This is a common vulnerability pattern in embedded devices where memory-safe programming practices may not be consistently applied due to resource constraints or legacy code bases.

Attack Vector

The attack vector is network-based, targeting the router's web management interface. An attacker would need to:

1. Gain access to the router's administrative web interface (typically requires network access and low-level authentication)
2. Submit a crafted HTTP request to the /boaform/formPing endpoint
3. Include an overly long or specially crafted value in the pingAddr parameter
4. The malformed input overflows the stack buffer, potentially overwriting return addresses or other critical stack data

The vulnerability is exploitable remotely without user interaction, though it requires low-level privileges (authenticated access to the diagnostic interface). The public availability of the exploit increases the likelihood of weaponization.

For detailed technical information about this vulnerability, refer to the GitHub Issue Discussion and the VulDB Entry.

Detection Methods for CVE-2026-2909

Indicators of Compromise

• Unusual HTTP POST requests to /boaform/formPing with abnormally long pingAddr parameter values
• Router crashes or unexpected reboots following diagnostic interface access
• Anomalous outbound network connections from the router after administrative interface usage
• Modified router configuration or unauthorized firmware changes

Detection Strategies

• Monitor network traffic for HTTP requests to /boaform/formPing containing excessively long parameter values (exceeding typical IP address or hostname lengths)
• Implement IDS/IPS rules to detect buffer overflow patterns targeting Tenda router endpoints
• Deploy network segmentation to isolate IoT devices and monitor cross-segment traffic for anomalies
• Review router access logs for suspicious administrative interface activity

Monitoring Recommendations

• Enable logging on the router if available and forward logs to a centralized SIEM
• Monitor for unexpected device behavior such as crashes, reboots, or configuration changes
• Implement network behavior analysis to detect unusual traffic patterns from the router
• Regularly audit devices on the network to ensure firmware versions are tracked and monitored

How to Mitigate CVE-2026-2909

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Implement firewall rules to block external access to the administrative interface on ports 80/443
• Consider disabling the web management interface if not required for operations
• Monitor for any available firmware updates from Tenda

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for firmware updates and security advisories. The vulnerability details are tracked in VulDB Entry #347218.

Workarounds

• Disable remote management access to the router's web interface
• Use access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
• Place the router behind a properly configured firewall that blocks unauthorized access to the management interface
• Consider replacing the affected device with a router from a vendor with a stronger security update track record if no patch becomes available

# Example: Restrict management interface access via iptables (on upstream firewall)
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 from trusted management subnet
iptables -I FORWARD -s <trusted_subnet> -d <router_ip> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <trusted_subnet> -d <router_ip> -p tcp --dport 443 -j ACCEPT