CVE-2026-24114: Tenda W20e Buffer Overflow Vulnerability

CVE-2026-24114 Overview

A critical buffer overflow vulnerability has been identified in Tenda W20E V4.0br_V15.11.0.6. The vulnerability stems from a failure to properly validate the pPortMapIndex parameter before passing it to the strcpy function, which can result in buffer overflows. This firmware vulnerability in the Tenda W20E enterprise router allows attackers to potentially compromise the device through network-based attacks without requiring authentication or user interaction.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially achieve full device compromise, including arbitrary code execution, denial of service, or complete system takeover on affected Tenda W20E routers.

Affected Products

• Tenda W20E Firmware version 15.11.0.6
• Tenda W20E Hardware version 4.0
• Tenda W20E V4.0br_V15.11.0.6

Discovery Timeline

• 2026-03-02 - CVE-2026-24114 published to NVD
• 2026-03-03 - Last updated in NVD database

Technical Details for CVE-2026-24114

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The root cause lies in the improper handling of user-controlled input when processing the pPortMapIndex parameter within the firmware's port mapping functionality.

When the firmware receives port mapping configuration requests, it processes the pPortMapIndex parameter without adequate bounds checking. The vulnerable code path directly uses the strcpy function to copy the parameter value into a fixed-size buffer, without verifying that the source data fits within the destination buffer's allocated memory space.

The network-accessible nature of this vulnerability means that remote attackers can trigger the overflow by sending specially crafted requests to the device. No authentication is required to exploit this vulnerability, and no user interaction is necessary, making it particularly dangerous for devices exposed to the internet or untrusted networks.

Root Cause

The vulnerability originates from insufficient input validation on the pPortMapIndex parameter. The firmware fails to verify the length of user-supplied data before performing a buffer copy operation using strcpy. This unsafe string handling function copies data until it encounters a null terminator, without regard for the destination buffer's size, leading to a classic stack or heap-based buffer overflow condition.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can craft malicious HTTP requests or management interface commands containing an oversized pPortMapIndex parameter value. When processed by the vulnerable router firmware, this triggers a buffer overflow condition.

Successful exploitation could allow an attacker to overwrite adjacent memory, potentially corrupting program control flow data such as return addresses or function pointers. This could lead to arbitrary code execution with the privileges of the web server process, typically running as root on embedded devices like routers.

For detailed technical information about this vulnerability, refer to the GitHub CVE Report and the Tenda Security Bulletin.

Detection Methods for CVE-2026-24114

Indicators of Compromise

• Unusual network traffic patterns to the router's management interface, particularly oversized HTTP requests
• Unexpected device reboots or instability that may indicate crash attempts
• Anomalous processes running on the router if shell access is available for inspection
• Changes to device configuration without administrator action

Detection Strategies

• Implement network intrusion detection rules to identify abnormally large pPortMapIndex parameter values in HTTP requests to Tenda devices
• Monitor for repeated connection attempts to the router's web management interface from unknown or suspicious IP addresses
• Deploy deep packet inspection to examine HTTP POST data targeting port mapping configuration endpoints
• Use firmware integrity monitoring to detect unauthorized modifications to the device

Monitoring Recommendations

• Enable and regularly review router access logs for suspicious activity patterns
• Configure network monitoring to alert on high-volume connection attempts to management interfaces
• Implement SIEM correlation rules to detect potential exploitation attempts across your network infrastructure
• Monitor for devices in your environment running Tenda W20E firmware version 15.11.0.6

How to Mitigate CVE-2026-24114

Immediate Actions Required

• Restrict access to the router's management interface to trusted internal networks only
• Implement firewall rules to block external access to the device's web administration ports
• Consider taking vulnerable devices offline if they cannot be protected or patched immediately
• Monitor network traffic for signs of exploitation attempts against affected devices

Patch Information

Consult the Tenda Security Bulletin for the latest patch availability and firmware update instructions. Organizations should prioritize updating to a patched firmware version as soon as one becomes available from the vendor.

Workarounds

• Disable remote management access and only administer the device from directly connected networks
• Place the router behind a properly configured firewall that restricts access to management interfaces
• Implement network segmentation to isolate vulnerable devices from critical infrastructure
• Consider replacing end-of-life or unsupported devices with actively maintained alternatives

# Example: Restrict management interface access using 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
# Only allow management from trusted admin subnet
iptables -I FORWARD -s <ADMIN_SUBNET> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT