CVE-2026-24108: Tenda W20e Firmware Buffer Overflow Flaw

CVE-2026-24108 Overview

A critical buffer overflow vulnerability has been identified in Tenda W20E firmware version V4.0br_V15.11.0.6. The vulnerability exists in the getMibPrefix function where the nptr parameter value is concatenated using sprintf without proper size validation. This allows remote attackers to exploit the vulnerability by controlling the nptr value, potentially leading to arbitrary code execution, system compromise, or denial of service conditions on affected devices.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability over the network without authentication, potentially achieving complete system compromise including confidentiality, integrity, and availability impacts.

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-2026-24108 published to NVD
• 2026-03-03 - Last updated in NVD database

Technical Details for CVE-2026-24108

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The flaw originates from the improper handling of user-controlled input within the getMibPrefix function. When an attacker provides a maliciously crafted nptr value, the function uses sprintf to concatenate this value without performing adequate boundary checks on the destination buffer size.

The network-accessible nature of this vulnerability means exploitation does not require prior authentication or user interaction, making it particularly dangerous for internet-exposed devices. Successful exploitation could enable attackers to overwrite adjacent memory locations, potentially hijacking program execution flow and achieving remote code execution with the privileges of the firmware process.

Root Cause

The root cause of CVE-2026-24108 stems from the unsafe use of the sprintf function in C programming. The getMibPrefix function accepts the nptr parameter from an external source and directly incorporates it into a string operation without validating that the resulting string will fit within the allocated buffer space. This represents a fundamental secure coding violation where input length validation is missing before performing memory operations.

Attack Vector

The attack vector is network-based, allowing remote exploitation without authentication. An attacker can craft a specially designed HTTP request or network packet containing an oversized nptr value targeting the vulnerable getMibPrefix function. When the firmware processes this malicious input, the sprintf operation writes beyond the bounds of the destination buffer, corrupting adjacent memory. This memory corruption can be leveraged to:

1. Crash the device causing denial of service
2. Overwrite function return addresses to redirect execution
3. Inject and execute arbitrary shellcode
4. Gain persistent access to the compromised router

Technical details and proof-of-concept information can be found in the GitHub PoC Repository and the Tenda Material Reference.

Detection Methods for CVE-2026-24108

Indicators of Compromise

• Unexpected device reboots or crashes indicating potential exploitation attempts
• Anomalous network traffic patterns targeting the device management interface
• Unusual process spawning or memory allocation patterns on the router
• Log entries showing malformed requests with oversized parameter values

Detection Strategies

• Implement network-based intrusion detection rules to identify oversized parameter values in requests to Tenda W20E devices
• Monitor for buffer overflow exploitation signatures in network traffic destined for device management ports
• Deploy SentinelOne Singularity to detect anomalous behavior patterns associated with memory corruption attacks
• Establish baseline network behavior for router management traffic and alert on deviations

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices to capture traffic to vulnerable routers
• Implement real-time alerting for connection attempts from untrusted sources to router management interfaces
• Configure network segmentation monitoring to detect lateral movement from potentially compromised network devices
• Regularly audit device firmware versions and maintain an inventory of vulnerable Tenda W20E deployments

How to Mitigate CVE-2026-24108

Immediate Actions Required

• Restrict network access to affected Tenda W20E devices by implementing firewall rules blocking management interface access from untrusted networks
• Disable remote management features if not operationally required
• Place vulnerable devices behind a VPN or additional network security controls
• Monitor for vendor security advisories and firmware updates from Tenda

Patch Information

At the time of publication, no official patch has been confirmed by the vendor. Organizations should monitor the Tenda Material Reference page for updated firmware releases that address this vulnerability. Until a patch is available, implementing the recommended workarounds and compensating controls is essential.

Workarounds

• Disable WAN-side management access to prevent remote exploitation from the internet
• Implement access control lists (ACLs) to restrict management interface access to trusted IP addresses only
• Deploy network segmentation to isolate vulnerable devices from critical network resources
• Consider replacing affected devices with alternative hardware if vendor remediation is not timely

# Configuration example - Network isolation via firewall rules
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP

# Restrict management access to specific admin IP
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP