CVE-2026-2186: Tenda RX3 Buffer Overflow Vulnerability

CVE-2026-2186 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda RX3 firmware version 16.03.13.11. The vulnerability exists in the fromSetIpMacBind function located in the /goform/SetIpMacBind file. Improper handling of the list argument allows remote attackers to trigger a stack-based buffer overflow condition. The exploit has been publicly disclosed and may be actively leveraged by threat actors targeting vulnerable router deployments.

Critical Impact

This vulnerability enables remote attackers to potentially execute arbitrary code or cause denial of service on affected Tenda RX3 routers by exploiting the stack-based buffer overflow through network-accessible attack vectors.

Affected Products

• Tenda RX3 Firmware version 16.03.13.11
• Tenda RX3 Hardware

Discovery Timeline

• 2026-02-08 - CVE-2026-2186 published to NVD
• 2026-02-10 - Last updated in NVD database

Technical Details for CVE-2026-2186

Vulnerability Analysis

The vulnerability resides in the fromSetIpMacBind function within the Tenda RX3 router firmware. This function processes user-supplied input through the list parameter when handling requests to /goform/SetIpMacBind. The firmware fails to properly validate the length of input data before copying it to a fixed-size stack buffer, creating a classic stack-based buffer overflow condition (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer).

When an attacker sends a specially crafted request with an oversized list parameter, the function writes beyond the allocated stack buffer boundaries. This can corrupt adjacent stack memory including saved return addresses and function pointers, potentially allowing attackers to hijack program execution flow.

Root Cause

The root cause is improper bounds checking in the fromSetIpMacBind function when handling the list argument. The firmware lacks adequate input validation to ensure that user-supplied data does not exceed the allocated buffer size on the stack. This is a common vulnerability pattern in embedded device firmware where performance constraints sometimes lead to omission of proper input sanitization routines.

Attack Vector

The attack can be performed remotely over the network by sending malicious HTTP requests to the router's web management interface. An attacker with low privileges can craft a request to the /goform/SetIpMacBind endpoint with a manipulated list parameter containing excessive data. No user interaction is required for exploitation. The attack requires network access to the router's management interface, which may be accessible from the local network or, in misconfigured deployments, from the internet.

The vulnerability allows for high impact to confidentiality, integrity, and availability of the affected device. Successful exploitation could result in complete device compromise, enabling attackers to execute arbitrary code, modify router configurations, intercept network traffic, or render the device inoperable.

Detection Methods for CVE-2026-2186

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/SetIpMacBind with abnormally large payloads
• Router crashes, reboots, or unresponsive behavior following network requests
• Unusual outbound connections from the router to unknown IP addresses
• Modified router configurations without administrator actions

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests to /goform/SetIpMacBind with oversized list parameters
• Implement network intrusion detection rules to flag anomalous payload sizes targeting Tenda device endpoints
• Deploy web application firewalls to inspect and block malformed requests to router management interfaces
• Review router logs for repeated authentication attempts or unusual administrative API calls

Monitoring Recommendations

• Enable logging on the router's management interface if supported
• Configure network monitoring tools to alert on traffic patterns consistent with buffer overflow exploitation attempts
• Regularly audit network traffic to and from IoT devices including routers
• Implement segmentation to isolate router management interfaces from untrusted network segments

How to Mitigate CVE-2026-2186

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Place affected routers behind a firewall that filters requests to /goform/SetIpMacBind
• Monitor for firmware updates from Tenda and apply patches as soon as available

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Organizations should monitor the Tenda Official Website for security updates and firmware releases. Additional technical details can be found in the GitHub Issue Discussion and VulDB Threat Report #344889.

Workarounds

• Configure firewall rules to block external access to the router's management interface on port 80/443
• Use access control lists (ACLs) to restrict management interface access to specific administrator workstations
• Consider replacing vulnerable devices with alternative hardware if patches are not forthcoming
• Implement network segmentation to limit the blast radius if a device is compromised

# Example: Block external access to router management (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 management only from trusted admin subnet
iptables -I FORWARD -s 192.168.1.0/24 -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT