CVE-2026-24115: Tenda W20e Firmware Buffer Overflow Flaw

CVE-2026-24115 Overview

A buffer overflow vulnerability has been discovered in Tenda W20E V4.0br_V15.11.0.6 firmware. The vulnerability exists due to a failure to validate the sizes of the gstup and gstdwn parameters before concatenating them into the gstruleQos buffer, which can lead to a buffer overflow condition. This flaw affects the QoS (Quality of Service) rule processing functionality and may allow remote attackers to execute arbitrary code or cause a denial of service on affected devices.

Critical Impact

This buffer overflow vulnerability can be exploited remotely without authentication, potentially allowing attackers to gain complete control over affected Tenda W20E routers or disrupt network services.

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-2026-24115 published to NVD
• 2026-03-03 - Last updated in NVD database

Technical Details for CVE-2026-24115

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 QoS rule processing component of the Tenda W20E firmware, where user-supplied input parameters gstup and gstdwn are concatenated into a destination buffer gstruleQos without proper bounds checking.

When an attacker provides oversized values for these parameters, the concatenation operation can write data beyond the allocated buffer boundaries, corrupting adjacent memory regions. Since this vulnerability is accessible via the network without requiring authentication, it presents a significant risk to organizations deploying these devices.

Root Cause

The root cause of CVE-2026-24115 is improper input validation in the firmware's QoS rule handling code. The vulnerable code path fails to verify that the combined length of gstup and gstdwn parameters does not exceed the size of the destination buffer gstruleQos. This oversight allows attackers to craft malicious requests containing oversized parameters that overflow the target buffer during the concatenation operation.

Buffer overflow vulnerabilities in embedded devices like routers are particularly dangerous because these devices often lack modern memory protection mechanisms such as ASLR (Address Space Layout Randomization) or stack canaries, making exploitation more reliable.

Attack Vector

The attack can be conducted remotely over the network without requiring any authentication or user interaction. An attacker would craft a malicious HTTP request targeting the QoS configuration interface of the Tenda W20E router, providing specially crafted values for the gstup and gstdwn parameters that exceed expected lengths.

When processed by the vulnerable firmware, these oversized parameters trigger the buffer overflow condition, potentially allowing the attacker to overwrite return addresses, function pointers, or other critical data structures. Successful exploitation could lead to arbitrary code execution with the privileges of the affected process, or denial of service through system crash.

For detailed technical analysis, refer to the GitHub CVE-2026-24115 Report and Tenda Security Material.

Detection Methods for CVE-2026-24115

Indicators of Compromise

• Unusual HTTP requests to QoS configuration endpoints containing abnormally long parameter values
• Router crashes, reboots, or unresponsive behavior following network requests
• Unexpected changes to router configuration or firmware
• Network traffic anomalies indicating potential command and control communication from the router

Detection Strategies

• Monitor HTTP traffic to Tenda W20E devices for requests with unusually long gstup or gstdwn parameters
• Implement network-based intrusion detection rules to flag buffer overflow attack patterns targeting embedded devices
• Deploy SentinelOne Singularity to detect and prevent exploitation attempts against vulnerable network infrastructure
• Conduct regular firmware version audits to identify devices running vulnerable firmware version 15.11.0.6

Monitoring Recommendations

• Enable logging on network security devices to capture traffic destined for Tenda W20E management interfaces
• Configure alerts for repeated connection attempts or unusual request patterns to router administration ports
• Implement network segmentation to isolate vulnerable devices from critical network segments
• Monitor for unauthorized firmware modifications or configuration changes on affected devices

How to Mitigate CVE-2026-24115

Immediate Actions Required

• Identify all Tenda W20E devices running firmware version 15.11.0.6 within your environment
• Restrict network access to the router's management interface to trusted IP addresses only
• Place vulnerable devices behind a properly configured firewall
• Monitor affected devices for signs of exploitation until patches can be applied
• Consider replacing affected devices if no firmware update is available from the vendor

Patch Information

At the time of publication, consult the Tenda Security Material for the latest firmware updates and security advisories. Organizations should regularly check for firmware updates from Tenda and apply patches as soon as they become available. Given the critical nature of this vulnerability, prioritize patching or replacing affected devices.

Workarounds

• Disable remote management access and only allow local administration of the device
• Implement strict firewall rules to block external access to the router's web interface
• Use network segmentation to isolate vulnerable routers from sensitive network resources
• Consider deploying an additional firewall or IPS in front of affected devices to filter malicious requests
• If possible, disable the QoS functionality until a patch is available

# Example firewall rule to restrict access to router management interface
# Replace 192.168.1.1 with your router's IP and 10.0.0.0/24 with trusted admin network
iptables -A INPUT -d 192.168.1.1 -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A INPUT -d 192.168.1.1 -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -d 192.168.1.1 -p tcp --dport 443 -j DROP