Executive Summary

CVE-2026-36770 is a stack-based buffer overflow vulnerability found in the Tenda W3 Wireless Router firmware version 1.0.0.3. It occurs in the ask_to_reboot function, which handles a user-controlled HTTP parameter named "GO". This parameter is unsafely concatenated into a fixed-size stack buffer using the sprintf function without proper bounds checking. When an attacker sends a crafted HTTP request with an excessively long "GO" parameter, it causes a stack overflow.

This overflow can crash the httpd service or reboot the device, resulting in a Denial of Service (DoS). Depending on the device's architecture and security protections like stack canaries, NX, and ASLR, it may also allow arbitrary code execution.

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Impact Analysis

This vulnerability can impact you by causing a Denial of Service (DoS) on the affected Tenda W3 Wireless Router. An attacker can exploit the stack overflow to crash the router's httpd service or force the device to reboot, disrupting network connectivity and availability.

In some cases, if the device's security protections are insufficient, the attacker might also execute arbitrary code, potentially leading to further compromise of the device.

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Detection Guidance

This vulnerability can be detected by monitoring for HTTP requests sent to the ask_to_reboot CGI handler that contain an unusually long or crafted "GO" parameter. Such requests may cause the device's httpd service to crash or the device to reboot unexpectedly.

A practical detection method is to capture and analyze HTTP traffic targeting the Tenda W3 Wireless Router's configuration interface, specifically looking for requests to the ask_to_reboot endpoint with the "GO" parameter.

• Use a network packet capture tool like tcpdump or Wireshark to filter HTTP requests to the router's IP on the ask_to_reboot CGI path.
• Example tcpdump command to capture suspicious requests: tcpdump -i <interface> -A 'tcp port 80 and (((ip dst <router_ip>) and (tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x474f3d))' where 0x474f3d corresponds to 'GO=' in ASCII.
• Alternatively, use curl or similar tools to test the endpoint by sending a crafted HTTP request with a long "GO" parameter and observe if the device crashes or reboots.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the ask_to_reboot CGI handler to trusted users only, such as by limiting access to the router's management interface via firewall rules or network segmentation.

Additionally, monitor the device for unexpected reboots or crashes that may indicate exploitation attempts.

If possible, disable or restrict the functionality of the ask_to_reboot endpoint until a firmware update addressing the vulnerability is available.

Contact the vendor for firmware updates or patches that fix the stack overflow vulnerability in the ask_to_reboot function.

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Compliance Impact

The provided information does not specify any direct impact of the CVE-2026-36770 vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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