CVE-2026-24113: Tenda W20e Firmware Buffer Overflow Flaw

CVE-2026-24113 Overview

A critical buffer overflow vulnerability has been discovered in Tenda W20E V4.0br_V15.11.0.6 router firmware. The vulnerability exists due to improper size validation when the user-controlled nptr parameter is passed into the getMibPrefix function and concatenated using sprintf. This allows remote attackers to potentially achieve arbitrary code execution or cause denial of service conditions on affected devices.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to execute arbitrary code, potentially taking complete control of the affected Tenda W20E router without requiring authentication.

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-2026-24113 published to NVD
• 2026-03-05 - Last updated in NVD database

Technical Details for CVE-2026-24113

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), commonly known as a classic buffer overflow. The flaw resides in the getMibPrefix function within the Tenda W20E firmware. When processing user-supplied input through the nptr parameter, the function uses sprintf for string concatenation without performing proper bounds checking on the input length.

The vulnerability is accessible over the network without requiring authentication or user interaction, making it particularly dangerous for internet-facing router deployments. Successful exploitation could result in complete compromise of confidentiality, integrity, and availability of the affected device.

Root Cause

The root cause of this vulnerability stems from unsafe string handling practices in the firmware's C code. The sprintf function is inherently unsafe as it does not perform bounds checking when writing to the destination buffer. When attacker-controlled data from the nptr parameter is concatenated into a fixed-size buffer, it can overflow the allocated memory space, corrupting adjacent memory regions including return addresses and function pointers.

Attack Vector

The attack can be performed remotely over the network. An attacker can craft a malicious request containing an oversized nptr value, which is then processed by the vulnerable getMibPrefix function. The oversized input overflows the destination buffer during the sprintf concatenation operation. By carefully crafting the overflow data, an attacker may be able to overwrite critical memory structures, potentially achieving code execution or causing the device to crash.

The vulnerability does not require any privileges or authentication to exploit, and no user interaction is needed. Technical details and proof-of-concept information can be found in the GitHub CVE-2026-24113 Report.

Detection Methods for CVE-2026-24113

Indicators of Compromise

• Unexpected router reboots or crashes indicating potential exploitation attempts
• Abnormally large HTTP request parameters in router access logs
• Unusual network traffic originating from the router to unknown external destinations
• Modified router configuration or firmware without administrator action

Detection Strategies

• Monitor network traffic for unusually large request payloads targeting Tenda W20E management interfaces
• Implement intrusion detection rules to flag oversized parameter values in HTTP requests to router endpoints
• Deploy network monitoring to detect buffer overflow exploitation patterns targeting embedded devices
• Review router logs for repeated crash events or unexpected service restarts

Monitoring Recommendations

• Enable comprehensive logging on network firewalls protecting Tenda router management interfaces
• Implement network segmentation to isolate IoT and router management networks
• Deploy endpoint detection solutions capable of monitoring embedded device behavior
• Establish baseline network behavior for router traffic to identify anomalies

How to Mitigate CVE-2026-24113

Immediate Actions Required

• Restrict network access to the Tenda W20E management interface to trusted IP addresses only
• Place the router behind a firewall and disable remote management if not required
• Monitor for firmware updates from Tenda addressing this vulnerability
• Consider replacing vulnerable devices if no patch becomes available

Patch Information

At the time of publication, refer to the Tenda Security Advisory for the latest patch information and firmware updates. Organizations should regularly check Tenda's official support channels for security updates addressing CVE-2026-24113.

Workarounds

• Disable remote management access to prevent network-based exploitation
• Implement strict access control lists (ACLs) limiting management interface access to specific administrator IP addresses
• Deploy a network firewall or intrusion prevention system (IPS) to filter malicious requests
• Consider network isolation for affected devices until a patch is available

# Example firewall rule to restrict router management access
# Allow only specific admin IP to access router management port
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP