CVE-2026-2187: Tenda RX3 Buffer Overflow Vulnerability

CVE-2026-2187 Overview

A critical stack-based buffer overflow vulnerability has been identified in the Tenda RX3 router firmware version 16.03.13.11. The vulnerability exists in the set_qosMib_list function within the /goform/formSetQosBand file, where improper handling of the list argument allows attackers to overflow the stack buffer. This firmware vulnerability can be exploited remotely over the network, potentially allowing attackers to execute arbitrary code or cause denial of service on affected devices.

Critical Impact

Remote attackers with low-level privileges can exploit this stack-based buffer overflow to potentially achieve code execution on vulnerable Tenda RX3 routers, compromising network security and enabling lateral movement within affected environments.

Affected Products

• Tenda RX3 Firmware version 16.03.13.11
• Tenda RX3 Router Hardware

Discovery Timeline

• 2026-02-08 - CVE-2026-2187 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-2187

Vulnerability Analysis

This vulnerability is a classic stack-based buffer overflow (CWE-119) that occurs in the QoS (Quality of Service) configuration functionality of the Tenda RX3 router. The vulnerable function set_qosMib_list processes user-supplied input from the list parameter without adequate bounds checking. When an attacker provides an oversized or specially crafted input to the list argument via the /goform/formSetQosBand endpoint, the function writes beyond the allocated stack buffer boundaries.

The attack can be executed remotely over the network, requires low-level privileges, and needs no user interaction. The potential impact includes complete compromise of confidentiality, integrity, and availability of the affected device. An exploit for this vulnerability has been disclosed publicly, increasing the risk of active exploitation.

Root Cause

The root cause of CVE-2026-2187 lies in insufficient input validation and bounds checking within the set_qosMib_list function. The function fails to properly verify the length of the list parameter before copying it to a fixed-size stack buffer. This memory safety oversight is common in embedded device firmware written in C/C++ where manual memory management is required. The absence of stack canaries or other runtime protections in the firmware exacerbates the exploitability of this vulnerability.

Attack Vector

The attack vector is network-based, targeting the web management interface of the Tenda RX3 router. An attacker can craft a malicious HTTP request to the /goform/formSetQosBand endpoint with an oversized list parameter. The exploitation flow involves:

1. Identifying a vulnerable Tenda RX3 router exposed to the network
2. Sending a crafted POST request to /goform/formSetQosBand with a malicious list parameter
3. Overflowing the stack buffer to overwrite return addresses or other critical data
4. Potentially achieving code execution or causing a denial of service condition

The vulnerability mechanism involves manipulating the list argument in the QoS configuration handler. When the set_qosMib_list function processes this input, it copies the data to a stack-allocated buffer without verifying that the input length does not exceed the buffer size. This allows an attacker to overwrite adjacent stack memory, including saved return addresses, potentially redirecting execution flow. For detailed technical analysis, refer to the GitHub Issue Discussion and VulDB entry.

Detection Methods for CVE-2026-2187

Indicators of Compromise

• Unusual HTTP POST requests to /goform/formSetQosBand containing abnormally long list parameter values
• Router crashes, reboots, or unresponsive web management interfaces following network activity
• Unexpected network traffic patterns or unauthorized configuration changes on Tenda RX3 devices
• Log entries showing repeated access attempts to QoS configuration endpoints

Detection Strategies

• Deploy network intrusion detection rules to identify HTTP requests with oversized parameters targeting /goform/formSetQosBand
• Monitor for buffer overflow attack signatures in web application firewall (WAF) logs
• Implement SentinelOne Singularity for IoT to detect anomalous behavior patterns on network devices
• Perform regular firmware version audits to identify devices running vulnerable version 16.03.13.11

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices to capture traffic to Tenda router management interfaces
• Configure alerts for repeated authentication attempts or unusual API calls to router configuration endpoints
• Implement network segmentation to isolate IoT devices including routers from critical network segments
• Deploy SentinelOne network visibility tools to monitor for exploitation attempts across the enterprise

How to Mitigate CVE-2026-2187

Immediate Actions Required

• Restrict network access to the Tenda RX3 web management interface to trusted IP addresses only
• Disable remote management if not required for operations
• Place vulnerable Tenda RX3 devices behind a properly configured firewall blocking external access to management ports
• Monitor Tenda's official channels for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no official patch has been released by Tenda for CVE-2026-2187. Organizations should monitor the Tenda Official Security Page for security updates and firmware releases. Consider replacing affected devices with alternative products if patches are not made available in a timely manner.

Workarounds

• Implement network access control lists (ACLs) to restrict access to the router's web interface from untrusted networks
• Configure a reverse proxy or web application firewall to filter requests containing oversized parameters
• Disable the QoS configuration feature if not operationally required until a patch is available
• Consider network isolation to limit the potential impact of a compromised router

# Example iptables rules to restrict access to router management interface
# Replace ROUTER_IP with your Tenda RX3 IP address
# Replace TRUSTED_NETWORK with your management network CIDR

# Block external access to web management port
iptables -A INPUT -d ROUTER_IP -p tcp --dport 80 -j DROP
iptables -A INPUT -d ROUTER_IP -p tcp --dport 443 -j DROP

# Allow only trusted network to access management interface
iptables -I INPUT -s TRUSTED_NETWORK -d ROUTER_IP -p tcp --dport 80 -j ACCEPT
iptables -I INPUT -s TRUSTED_NETWORK -d ROUTER_IP -p tcp --dport 443 -j ACCEPT