CVE-2026-2906: Tenda HG9 Buffer Overflow Vulnerability

CVE-2026-2906 Overview

CVE-2026-2906 is a stack-based buffer overflow vulnerability in the Tenda HG9 router running firmware version 300001138. The flaw resides in the Samba Configuration Endpoint accessed through /boaform/formSamba. Attackers can manipulate the sambaCap argument to corrupt memory on the device stack. The vulnerability is exploitable over the network and a public exploit has been released, raising the likelihood of opportunistic attacks against exposed devices. The weakness is classified under CWE-119, improper restriction of operations within the bounds of a memory buffer.

Critical Impact
Remote attackers with low privileges can trigger memory corruption against the HG9 web management interface, potentially leading to code execution or full device compromise.

Affected Products

Tenda HG9 router (hardware)
Tenda HG9 firmware version 300001138
Samba Configuration Endpoint at /boaform/formSamba

Discovery Timeline

2026-02-22 - CVE-2026-2906 published to NVD
2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2906

Vulnerability Analysis

The vulnerability exists within the request handler for the /boaform/formSamba endpoint on the Tenda HG9 device web management interface. This endpoint processes Samba file-sharing configuration requests submitted from the administrative panel. The sambaCap parameter is copied into a fixed-size stack buffer without proper length validation. Supplying an oversized value overflows the buffer and corrupts adjacent stack memory, including saved return addresses and frame pointers. Because the embedded web server boa typically runs with elevated privileges on these consumer routers, successful exploitation can yield control of the device. The public release of exploit details lowers the barrier to attack, and similar Tenda flaws have been observed in opportunistic botnet recruitment campaigns.

Root Cause

The root cause is missing bounds checking on attacker-supplied input before a stack copy operation, consistent with [CWE-119]. The handler trusts the length of sambaCap provided in the HTTP request body and writes it into a local buffer sized for legitimate configuration values. No length validation, truncation, or use of length-bounded copy primitives such as strncpy with appropriate sizing protects the buffer.

Attack Vector

Exploitation requires network reachability to the HG9 web interface and a low-privilege authenticated session. An attacker sends a crafted POST request to /boaform/formSamba with a sambaCap argument longer than the destination buffer. The overflow overwrites saved control data on the stack, enabling control-flow hijack. Devices that expose the management interface to the WAN or to untrusted LAN segments are at the highest risk.

No verified proof-of-concept code is included here. Refer to the GitHub Issue Discussion and VulDB #347215 for technical references.

Detection Methods for CVE-2026-2906

Indicators of Compromise

HTTP POST requests to /boaform/formSamba containing unusually long sambaCap parameter values
Unexpected reboots, crashes, or boa web server restarts on the HG9 device
New outbound connections from the router to unknown command-and-control infrastructure following configuration changes

Detection Strategies

Inspect network traffic for HTTP requests to /boaform/formSamba where the sambaCap field exceeds expected length thresholds, typically a few hundred bytes
Deploy intrusion detection signatures that match oversized parameter values in boaform POST bodies
Correlate web management interface access logs with subsequent anomalous device behavior

Monitoring Recommendations

Restrict and log all access to the router administrative interface from internal management hosts only
Forward router syslog data to a centralized log platform for retention and analysis
Alert on changes to Samba configuration parameters outside of scheduled change windows

How to Mitigate CVE-2026-2906

Immediate Actions Required

Disable remote WAN administration on the Tenda HG9 device until a patch is verified
Restrict LAN access to the web management interface to a dedicated administrative subnet
Rotate administrative credentials to limit reuse of low-privilege accounts required for exploitation
Disable the Samba service on the device if file sharing is not required

Patch Information

At the time of publication, the Tenda Official Website has not published a fixed firmware release for HG9 version 300001138. Monitor vendor advisories and the VulDB CTI Reference #347215 for updates. Apply firmware updates as soon as they are released and validate device integrity afterward.

Workarounds

Place the HG9 router behind an upstream firewall that blocks inbound HTTP and HTTPS to the management interface
Segment Samba and management traffic onto a VLAN inaccessible to untrusted hosts
Replace affected devices with supported hardware if the vendor does not issue a timely patch

bash

# Example: block inbound access to the HG9 management interface from untrusted networks
iptables -A FORWARD -d <hg9_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <hg9_ip> -p tcp --dport 443 -j DROP