CVE-2026-36809: Tenda W15E Buffer Overflow DoS Vulnerability

CVE-2026-36809 Overview

CVE-2026-36809 is a buffer overflow vulnerability in Shenzhen Tenda Technology Co., Ltd Tenda W15E router firmware version v15.11.0.10. The flaw resides in the webAuthWhiteID parameter of the formModifyWebAuthWhiteUser function. Remote attackers can trigger a Denial of Service (DoS) condition by sending a crafted HTTP request to the affected device. The vulnerability is classified under [CWE-120] (Buffer Copy without Checking Size of Input). No authentication or user interaction is required to exploit this flaw.

Critical Impact
Unauthenticated attackers can crash the Tenda W15E router remotely via a single HTTP request, disrupting network availability for all connected users.

Affected Products

Shenzhen Tenda Technology Co., Ltd Tenda W15E
Firmware version v15.11.0.10
formModifyWebAuthWhiteUser function handling the webAuthWhiteID parameter

Discovery Timeline

2026-06-09 - CVE-2026-36809 published to NVD
2026-06-10 - Last updated in NVD database

Technical Details for CVE-2026-36809

Vulnerability Analysis

The Tenda W15E router exposes a web management interface that processes authentication whitelist modifications through the formModifyWebAuthWhiteUser handler. This function accepts user-controlled input via the webAuthWhiteID HTTP parameter without enforcing proper length validation. When an attacker submits an oversized value, the function copies the data into a fixed-size stack buffer, overwriting adjacent memory regions. The resulting memory corruption causes the httpd service to crash, producing a Denial of Service condition. The router's web administration becomes unreachable and network routing functions may be interrupted until the device is restarted.

Root Cause

The root cause is the absence of bounds checking on the webAuthWhiteID parameter before it is copied into a stack-allocated buffer. This pattern matches [CWE-120], where the destination buffer's capacity is not validated against the source input length. Embedded router firmware frequently relies on unsafe C string operations such as strcpy or sprintf, which propagate untrusted input directly into fixed buffers without size constraints.

Attack Vector

An attacker on the network sends a crafted HTTP POST request to the router's web management endpoint with a malformed webAuthWhiteID value. No credentials or user interaction are required. The crafted payload triggers the buffer overflow, terminating the web server process and disrupting management access. The vulnerability is exploitable from any network-adjacent position that can reach the router's HTTP interface. Refer to the GitHub PoC Repository for technical details on the exploitation primitive.

Detection Methods for CVE-2026-36809

Indicators of Compromise

Unexpected reboots or crashes of the Tenda W15E httpd service
HTTP POST requests to formModifyWebAuthWhiteUser containing abnormally long webAuthWhiteID parameter values
Repeated loss of router web management availability without administrator action
Network connectivity disruptions correlated with inbound HTTP traffic to the router's management port

Detection Strategies

Inspect HTTP traffic destined for the router for requests targeting formModifyWebAuthWhiteUser with parameter lengths exceeding expected sizes
Deploy intrusion detection signatures that flag oversized values in webAuthWhiteID POST parameters
Monitor router uptime and service availability metrics for anomalous restart patterns

Monitoring Recommendations

Enable logging on network perimeter devices to capture HTTP requests directed at internal management interfaces
Correlate router crash events with preceding HTTP request patterns in centralized logging platforms
Restrict and monitor administrative access to router web interfaces from untrusted network segments

How to Mitigate CVE-2026-36809

Immediate Actions Required

Restrict access to the Tenda W15E web management interface to trusted management VLANs only
Disable remote (WAN-side) management access if not strictly required for operations
Monitor vendor channels for an official firmware update addressing CVE-2026-36809

Patch Information

No official patch information is available in the NVD record at the time of publication. Administrators should consult Shenzhen Tenda Technology Co., Ltd directly for firmware updates addressing the formModifyWebAuthWhiteUser buffer overflow. Until a patch is released, network-level mitigations are required.

Workarounds

Place the Tenda W15E behind a network firewall that filters HTTP requests containing oversized parameter values
Implement access control lists restricting which IP addresses can reach the router's web management port
Segment the router management interface onto a dedicated administrative network isolated from general user traffic
Consider replacing affected devices with supported hardware if vendor updates are not forthcoming

bash

# Example: restrict router management access via upstream firewall (iptables)
iptables -A FORWARD -p tcp --dport 80 -d <router_ip> -s <mgmt_subnet> -j ACCEPT
iptables -A FORWARD -p tcp --dport 80 -d <router_ip> -j DROP
iptables -A FORWARD -p tcp --dport 443 -d <router_ip> -s <mgmt_subnet> -j ACCEPT
iptables -A FORWARD -p tcp --dport 443 -d <router_ip> -j DROP