CVE-2026-2906: Tenda HG9 Buffer Overflow Vulnerability

CVE-2026-2906 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda HG9 firmware version 300001138. The vulnerability exists in the Samba Configuration Endpoint, specifically within the /boaform/formSamba component. Exploitation occurs through manipulation of the sambaCap argument, which fails to properly validate input length before copying data to a fixed-size stack buffer.

This vulnerability allows remote authenticated attackers to execute arbitrary code on affected devices, potentially leading to complete device compromise, network pivoting, and persistent access to the target network infrastructure.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to achieve code execution on Tenda HG9 routers. The public availability of exploit information increases the risk of widespread exploitation targeting home and small business networks.

Affected Products

• Tenda HG9 Firmware version 300001138
• Tenda HG9 Hardware devices running vulnerable firmware

Discovery Timeline

• February 22, 2026 - CVE-2026-2906 published to NVD
• February 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2906

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which encompasses the broader category of buffer overflow vulnerabilities. The flaw resides in the Samba Configuration Endpoint handler within the Tenda HG9 router firmware.

When processing HTTP requests to /boaform/formSamba, the firmware fails to properly validate the length of the sambaCap parameter before copying it into a stack-allocated buffer. This absence of bounds checking allows an attacker to supply an oversized input that overwrites adjacent stack memory, including saved return addresses and other critical data structures.

The network-accessible nature of this endpoint means that any authenticated user on the network can potentially trigger the vulnerability. Given that many router deployments use default or weak credentials, the authentication requirement presents a relatively low barrier to exploitation.

Root Cause

The root cause of this vulnerability is the lack of proper input validation and bounds checking in the /boaform/formSamba endpoint handler. The firmware directly copies user-supplied data from the sambaCap parameter into a fixed-size buffer on the stack without verifying that the input length does not exceed the buffer's capacity. This is a classic example of improper memory safety practices in embedded firmware development.

Attack Vector

The attack is network-based and can be launched remotely against the router's web management interface. An attacker with valid credentials (or exploiting default credentials) can send a specially crafted HTTP request to the /boaform/formSamba endpoint with an oversized sambaCap parameter value. The malicious payload overwrites stack memory, allowing the attacker to hijack program execution flow.

A successful exploit could result in:

• Arbitrary code execution with router privileges
• Complete device compromise
• Modification of router configuration and DNS settings
• Network traffic interception and manipulation
• Lateral movement to other network devices

The vulnerability is particularly concerning as the exploit details have been publicly released, increasing the likelihood of active exploitation in the wild.

Detection Methods for CVE-2026-2906

Indicators of Compromise

• Unusual HTTP POST requests to /boaform/formSamba with abnormally large sambaCap parameter values
• Router crashes, reboots, or unexpected behavior following web management access
• Unauthorized configuration changes to Samba or other router settings
• Suspicious outbound connections from the router to unknown IP addresses

Detection Strategies

• Monitor web server access logs on Tenda HG9 devices for requests to /boaform/formSamba with parameter lengths exceeding normal thresholds
• Implement network intrusion detection signatures to identify buffer overflow attack patterns targeting this endpoint
• Deploy behavioral analysis to detect anomalous router activity such as unexpected process spawning or network connections
• Utilize SentinelOne Singularity for IoT to identify and alert on exploitation attempts targeting vulnerable network devices

Monitoring Recommendations

• Enable verbose logging on the router's web management interface if supported
• Implement network segmentation to isolate IoT and network infrastructure devices from general user networks
• Deploy network traffic analysis solutions to monitor for suspicious patterns targeting router management interfaces
• Regularly audit router configurations for unauthorized changes

How to Mitigate CVE-2026-2906

Immediate Actions Required

• Disable remote web management access to the Tenda HG9 router if not strictly required
• Change default administrator credentials to strong, unique passwords
• Restrict web management interface access to trusted IP addresses or internal networks only
• Monitor for firmware updates from Tenda that address this vulnerability
• Consider network segmentation to isolate vulnerable devices

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 that address CVE-2026-2906. Additional technical details are available in the GitHub Issue Discussion and VulDB Entry #347215.

Workarounds

• Disable the web management interface entirely if remote administration is not needed
• Configure firewall rules to block external access to the router's management ports
• Place the router behind a hardware firewall or network security appliance that can filter malicious requests
• If possible, isolate the device from production networks until a patch is available
• Consider replacing the affected device with a router from a vendor with a stronger security update track record

# Example firewall rule to restrict web management access (network firewall)
# Block external access to router management interface on port 80/443
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 trusted management IP
iptables -I FORWARD -s <trusted_admin_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT