CVE-2026-2905: Tenda HG9 Buffer Overflow Vulnerability

CVE-2026-2905 Overview

CVE-2026-2905 is a stack-based buffer overflow affecting the Tenda HG9 router running firmware version 300001138. The flaw resides in an unspecified function within /boaform/formWlanSetup, which handles the device's Wireless Configuration Endpoint. Attackers can trigger the overflow by manipulating the ssid parameter, corrupting adjacent stack memory. The issue is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). Exploit details have been disclosed publicly through a GitHub issue tracker and the VulDB submission system, increasing exposure for unpatched devices.

Critical Impact
Authenticated remote attackers can corrupt stack memory through the ssid parameter, potentially leading to arbitrary code execution or full device compromise on Tenda HG9 routers.

Affected Products

Tenda HG9 router (hardware)
Tenda HG9 firmware version 300001138
Wireless Configuration Endpoint at /boaform/formWlanSetup

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

The vulnerability exists in the web-based administration interface served by the embedded boa HTTP server on the Tenda HG9. When a user submits a wireless configuration update, the request reaches the /boaform/formWlanSetup handler. The handler copies the user-supplied ssid argument into a fixed-size stack buffer without enforcing a length limit. An oversized ssid value overruns the buffer and overwrites adjacent stack data, including saved registers and the return address.

The attack is reachable across the network and requires low-privilege authentication based on the published vector. Public disclosure on GitHub and VulDB has lowered the technical barrier for exploitation, and EPSS data places initial exploitation probability in the lower tier.

Root Cause

The root cause is missing bounds validation on the ssid form parameter before it is copied into a stack-allocated buffer. The handler relies on unsafe string operations rather than length-checked alternatives such as strncpy with proper truncation. Embedded MIPS or ARM binaries in Tenda HG9 firmware typically lack modern stack protections like stack canaries and ASLR, allowing predictable return address overwrites.

Attack Vector

An attacker with access to the router's management interface, either on the local network or remotely if the web UI is exposed, sends a crafted HTTP POST request to /boaform/formWlanSetup containing an oversized ssid value. The malformed value overflows the stack buffer during configuration parsing. Successful exploitation can produce a denial of service through process crash, or arbitrary code execution if the attacker controls the return address with a valid payload. Refer to the GitHub Issue Discussion for the disclosed proof-of-concept details.

Detection Methods for CVE-2026-2905

Indicators of Compromise

HTTP POST requests to /boaform/formWlanSetup containing abnormally long ssid parameter values exceeding typical SSID length limits (32 characters).
Unexpected reboots, watchdog resets, or boa HTTP daemon crashes on Tenda HG9 routers.
Configuration changes to wireless settings that do not correlate with administrator activity.

Detection Strategies

Inspect web server access logs and network traffic for POST requests targeting /boaform/formWlanSetup with payloads containing non-printable characters or shellcode-like byte sequences in the ssid field.
Deploy network intrusion detection signatures that flag HTTP requests to Tenda management endpoints with ssid values longer than 64 bytes.
Monitor for repeated authentication attempts followed by configuration form submissions from the same source IP.

Monitoring Recommendations

Forward router system logs and web access logs to a centralized SIEM for correlation with authentication events.
Alert on connectivity loss or device reboots affecting Tenda HG9 routers in the asset inventory.
Track outbound connections originating from the router itself, which would indicate post-exploitation command-and-control activity.

How to Mitigate CVE-2026-2905

Immediate Actions Required

Restrict access to the router's web administration interface to trusted management VLANs and disable WAN-side administrative access.
Change default administrator credentials on all Tenda HG9 devices to reduce the impact of the low-privilege authentication requirement.
Inventory deployed Tenda HG9 routers and identify those running firmware version 300001138.
Monitor the Tenda Official Website for a vendor-issued firmware update addressing this issue.

Patch Information

At the time of publication, Tenda has not released a security patch addressing CVE-2026-2905. The vulnerability was disclosed through the VulDB CTI ID #347214 and a public GitHub Issue Discussion. Administrators should track the VulDB record and the vendor advisory page for firmware updates.

Workarounds

Place affected Tenda HG9 routers behind a network firewall that blocks inbound HTTP and HTTPS requests to the management interface from untrusted networks.
Disable remote management features in the router configuration so that the /boaform/ endpoints are only reachable from the LAN side.
Apply access control lists that limit which internal hosts can reach the router's web interface.
Where feasible, replace affected devices with hardware that receives active vendor security support.

bash

# Example iptables rule on an upstream gateway to block external access
# to the Tenda HG9 management interface (replace ROUTER_IP accordingly)
iptables -A FORWARD -d ROUTER_IP -p tcp --dport 80 -i wan0 -j DROP
iptables -A FORWARD -d ROUTER_IP -p tcp --dport 443 -i wan0 -j DROP