CVE-2026-36810: Tenda W15E Buffer Overflow DoS Vulnerability

Technical summary

CVE-2026-36810 is a classic stack-based buffer overflow (CWE-120) in the formPortalAuth function of Tenda W15E firmware v15.11.0.10. The gotoUrl HTTP parameter lacks proper bounds checking, allowing an attacker to overflow the allocated buffer with crafted input. This memory corruption causes immediate denial of service when the malformed request is processed. The CVSS 3.1 vector (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects network-accessible exploitation with no prerequisites, resulting in high impact to availability.

Business impact

Router availability directly affects business continuity for organizations relying on Tenda W15E devices for network access. A DoS attack renders the device unresponsive, severing internet connectivity until manual intervention restores the router. For small offices, remote locations, or backup network segments using this hardware, such outages can halt operations, interrupt cloud service access, and disrupt employee productivity. The low barrier to exploitation—requiring only an HTTP request and no authentication—makes this a practical denial-of-service vector against organizations unable to quickly replace affected devices.

Affected systems

Tenda W15E router running firmware version 15.11.0.10 is confirmed vulnerable. Organizations should verify their device firmware version via the router's web interface or management console. Tenda firmware versions are typically displayed under System Settings or Device Information. The vulnerability may affect earlier or concurrent firmware branches; verify against Tenda's official advisory for a complete list of impacted versions and device SKUs.

Exploitability

The vulnerability is highly exploitable in real-world conditions. No authentication, no user interaction, and no special network position is required—an attacker on the internet can trigger the crash with a single HTTP request. Crafting the malicious gotoUrl payload requires understanding buffer offset calculations, but this is straightforward for competent attackers. The attack succeeds reliably and can be automated for mass scanning or targeted campaigns. However, the impact is limited to temporary unavailability; the router recovers after rebooting.

Remediation

Immediately identify and inventory all Tenda W15E devices in your network. Contact Tenda support or check their official website for a firmware update that patches the buffer overflow in formPortalAuth. If a patch is available, schedule a maintenance window to upgrade affected routers. Prioritize devices that are internet-facing, serve critical functions, or lack redundant connectivity. Until patching is complete, implement compensating controls: restrict HTTP access to the router's web interface using a firewall, enable IP whitelisting on the device if available, or isolate the router behind an authenticated gateway.

Patch guidance

Consult Tenda's official security advisory and product support portal for the patched firmware version number and release date. Download firmware directly from Tenda's website and follow their documented update procedure for the W15E model. Do not use third-party repositories. If no patch is currently available, subscribe to Tenda's security notifications to be alerted when one is released. Document the firmware version before and after patching for compliance tracking. Test the update in a non-production environment if possible before deploying across your organization.

Detection guidance

Monitor network traffic to Tenda W15E devices for HTTP requests with abnormally long or malformed gotoUrl parameter values. Web application firewalls (WAF) and intrusion detection systems (IDS) should be configured to alert on oversized query parameters sent to web interfaces on router ports (typically 80, 443, or 8080). Enable verbose logging on the router if available; buffer overflow attempts may be recorded in access logs or system logs with anomalous request patterns. Correlate alerts with router uptime; unexpected reboots or service restarts on W15E devices warrant investigation. Network segmentation that isolates router management interfaces from untrusted sources will reduce exposure.

Why prioritize this

This vulnerability merits immediate action despite being non-exploitative for data theft. The CVSS 7.5 HIGH score reflects the ease of exploitation and lack of prerequisites—any internet-connected attacker can trigger DoS at will. The simplicity of the attack payload and the prevalence of Tenda W15E devices in SMB and branch office deployments create a broad target surface. While individual outages are temporary, repeated or coordinated attacks can disrupt business operations and damage organizational reputation. Prioritize patching based on device criticality: internet-facing routers and those without redundancy should be updated first.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) is driven by a network vector (AV:N), low attack complexity (AC:L), no privilege or user interaction required (PR:N, UI:N), and significant impact to availability (A:H). The vector yields no confidentiality or integrity impact (C:N, I:N), which prevents an even higher score. In practical terms, this scores as HIGH because any remote attacker can reliably crash the device; however, it does not escalate to CRITICAL because the impact is limited to availability and recovery is automatic upon reboot.

Frequently asked questions