CVE-2026-36811: Tenda W15E Buffer Overflow DoS Vulnerability – Patch & Mitigation Guide

Technical summary

CVE-2026-36811 is a classic stack-based or heap-based buffer overflow (CWE-120: Buffer Copy without Checking Size of Input) in the Tenda W15E v15.11.0.10 firmware. The vulnerability resides in the formDelwebAuthPic function, where user-supplied input in the 'picName' parameter is copied into a fixed-size buffer without adequate length validation. This allows an attacker to overflow the buffer boundary and overwrite adjacent memory, resulting in denial of service through application crash or memory corruption. The attack vector is network-based with low complexity and requires no authentication or user interaction.

Business impact

For organizations deploying Tenda W15E routers in production environments, this vulnerability introduces operational risk through potential network disruption. An unauthenticated attacker can remotely crash the router, causing loss of connectivity for connected devices and services relying on the router's availability. In critical deployments—such as remote office connectivity, IoT network infrastructure, or backup WAN links—an exploitable DoS condition could result in significant downtime. The lack of authentication requirements means exposure is broad if the device is internet-facing or accessible from untrusted networks.

Affected systems

Tenda W15E wireless router firmware version 15.11.0.10 is confirmed vulnerable. Organizations should verify whether they operate this specific firmware version in their deployed Tenda router fleet. Firmware version numbers prior to or after 15.11.0.10 may also be affected; validation against Tenda's security advisory and firmware release notes is strongly recommended to determine the full scope of affected versions within your environment.

Exploitability

This vulnerability is practical to exploit. The attack requires only network access to the router's HTTP interface and no special privileges or credentials. An attacker can craft a malicious HTTP request with an oversized or specially formatted 'picName' parameter and send it to the vulnerable formDelwebAuthPic endpoint. The low complexity and absence of user interaction barriers mean the exploit can be automated and delivered at scale. However, this remains a denial-of-service vulnerability; it does not appear to enable arbitrary code execution or unauthorized access.

Remediation

The primary remediation is to update the Tenda W15E firmware to a patched version released by Shenzhen Tenda Technology Co., Ltd. Consult Tenda's official security advisory and firmware download portal to identify the correct patched firmware version for your router model. Until patching is possible, interim mitigations include restricting network access to the router's HTTP management interface by limiting inbound connections to trusted IP addresses, disabling remote management if not required, and isolating the router behind a properly configured firewall.

Patch guidance

Visit Tenda's official support website and navigate to the W15E product page to download the latest available firmware. Follow Tenda's firmware update procedure carefully, which typically involves accessing the router's web interface and uploading the new firmware image. Before applying any patch in a production environment, test the update in a non-critical router or lab setting to ensure compatibility and stable operation. Document your current firmware version and the version you are upgrading to for audit and compliance purposes. If automated firmware update mechanisms are available through the router, verify they are enabled and configured appropriately.

Detection guidance

Monitor network traffic for HTTP requests to the router's management interface targeting the formDelwebAuthPic function with unusually long or malformed 'picName' parameter values. Inspect router logs for unexpected crashes, resets, or HTTP errors correlating with suspicious requests. Organizations with router intrusion detection or WAF capabilities should create rules to flag excessively long parameter values in picName fields. Router syslog and management interface logs should be retained and reviewed regularly. If available, enable verbose logging on the affected Tenda device to capture request details that may indicate exploitation attempts.

Why prioritize this

With a CVSS score of 7.5 (HIGH), this vulnerability merits prompt attention in security patch cycles. The combination of network accessibility, zero authentication requirements, and availability impact on network infrastructure justifies elevated priority. While not a confidentiality or integrity threat, operational disruption in a router—a critical trust boundary device—can cascade across dependent services and users. Organizations running Tenda W15E should prioritize patch deployment or compensating controls within 1-2 weeks of patch availability.

Risk score, explained

The CVSS 3.1 score of 7.5 reflects the vulnerability's HIGH severity through the following attributes: Attack Vector (AV:N) indicates the router is reachable over the network from an unauthenticated perspective; Attack Complexity (AC:L) means exploitation is straightforward with no special conditions; Privileges Required (PR:N) and User Interaction (UI:N) confirm no authentication or social engineering is necessary. Availability Impact (A:H) captures the denial-of-service consequence, while Confidentiality and Integrity impacts are None (C:N, I:N) because this is not an information disclosure or code execution vulnerability. The absence of scope change (S:U) reflects that impact is limited to the vulnerable service itself.

Frequently asked questions