CVE-2026-36793: Tenda W3 Router Stack Overflow DoS Vulnerability

Technical summary

CVE-2026-36793 is a stack buffer overflow in the formwrlSSIDset function of Tenda W3 Wireless Router v1.0.0.3(2204). The vulnerability stems from insufficient bounds checking on the mit_ssid and mis_ssid_index parameters when processing HTTP requests to the router's web interface. Stack buffer overflows occur when user-supplied data exceeds the allocated memory space on the call stack, potentially overwriting adjacent memory and causing application crashes or, in some scenarios, enabling code execution. In this case, the vulnerability manifests as denial of service. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects network-accessible attack surface, low complexity, no privileges required, and complete availability impact.

Business impact

An attacker exploiting this vulnerability can remotely force the Tenda W3 router to crash, rendering it unable to route traffic. For organizations or homes relying on this router for network connectivity, the impact is immediate service disruption. If the router is not monitored for availability or lacks automatic recovery mechanisms, downtime could extend until manual intervention restarts the device. In enterprise deployments where this router model might serve as an edge or branch device, such outages disrupt employee productivity and potentially interrupt critical operations. The vulnerability does not compromise confidentiality or integrity of data in transit, but availability impact alone constitutes significant operational risk.

Affected systems

Tenda W3 Wireless Router firmware version 1.0.0.3(2204) is confirmed vulnerable. Organizations should check their deployed Tenda W3 units for this specific firmware version. Tenda has not provided a list of affected firmware versions beyond the one mentioned; users running older or newer versions should verify whether patches or firmware updates address this issue by consulting the vendor advisory and release notes.

Exploitability

This vulnerability is straightforward to exploit. The attack requires only network access to the router's HTTP interface—a capability any device on the network or, if the router's web management interface is exposed to the internet, any remote attacker can achieve. No authentication is required, and no user interaction is needed. The simplicity and lack of prerequisites make this a high-priority concern, though it is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, meaning active exploitation in the wild has not been formally documented at the time of publication.

Remediation

Firmware patching is the primary remediation. Users should immediately check Tenda's support website for an updated firmware version addressing CVE-2026-36793 and apply it to their W3 routers. In parallel, network segmentation can limit exposure: restrict access to the router's web management interface to trusted administrative networks only, and disable remote management if it is enabled and not required. For affected organizations, prioritize patching devices exposed to untrusted networks or used in critical connectivity paths.

Patch guidance

Consult the official Tenda support portal and security advisories to identify the patched firmware version for the W3 router. Firmware updates for Tenda routers are typically available through the device's web interface under system settings or via the manufacturer's website. Before deploying any firmware update in a production environment, test it in a non-critical setting to ensure compatibility and stability. Document the firmware version before and after the update for audit purposes.

Detection guidance

Monitor router logs for HTTP requests containing unusually long or malformed SSID parameters (mit_ssid or mis_ssid_index fields). Network-based intrusion detection systems (IDS) can be configured to alert on suspicious HTTP requests to the router's management interface. Endpoint detection and response (EDR) tools on devices managing the router may flag unexpected crashes or restarts of the management process. Regular availability monitoring of the router (ping, HTTP health checks) can detect DoS events. Additionally, implement network access controls to limit which devices and IP ranges can reach the router's web interface.

Why prioritize this

This vulnerability merits high-priority attention due to its network-accessible nature, lack of authentication requirements, and immediate availability impact. While not yet documented in active exploitation campaigns, the low barrier to entry and potential for widespread disruption in networks using Tenda W3 routers mean it should be addressed promptly. Organizations should prioritize patching before the vulnerability becomes weaponized.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) reflects a network-accessible vulnerability with low attack complexity and complete loss of availability. The absence of confidentiality and integrity impact prevents a CRITICAL rating, but the ease of exploitation and network-wide consequences justify the HIGH severity classification. For a small office or home router, availability loss is disruptive; for a business-critical edge device, it is severe.

Frequently asked questions