Stack-Based Buffer Overflow in Tenda BE12 Pro

Executive Summary

CVE-2026-15696 is a stack-based buffer overflow vulnerability in the Tenda BE12 Pro router, specifically in firmware version 16.03.66.23. The issue occurs in the `fromVirtualSer` function within the `/goform/VirtualSer` endpoint.

The vulnerability arises because the function uses the unsafe `sprintf` function to write user-controlled input from the `page` parameter into a fixed-size 256-byte buffer without performing any length checks. This allows an attacker to provide oversized input that overflows the buffer, overwriting adjacent memory.

• The attack can be launched remotely without requiring authentication.
• Exploitation can lead to application crashes, memory corruption, or arbitrary code execution.
• Public exploits for this vulnerability exist and may be used by attackers.

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Detection Guidance

To detect the CVE-2026-15696 vulnerability on your network or system, you can check if the Tenda BE12 Pro router with firmware version 16.03.66.23 is present. The vulnerability exists in the `/goform/VirtualSer` endpoint, which can be exploited via a crafted POST request with an oversized `page` parameter.

• Identify Tenda BE12 Pro routers on your network by scanning for devices with the manufacturer 'Tenda' or checking for the specific model and firmware version. Tools like Nmap can be used with commands such as: `nmap -O <IP_range> --script http-title` to detect Tenda devices.
• Check the firmware version of the Tenda BE12 Pro router by accessing its web interface or using commands like: `curl http://<router_IP>/goform/getSysTools?random=0.123456789` to retrieve version information.
• Test for the vulnerability by sending a crafted POST request to the `/goform/VirtualSer` endpoint with an oversized `page` parameter. For example, using a Python script or `curl` command: `curl -X POST http://<router_IP>/goform/VirtualSer -d "page=<long_string_of_256+_characters>"`. If the router crashes or behaves unexpectedly, it may be vulnerable.

Note that testing for this vulnerability may disrupt router functionality, so it should be done in a controlled environment.

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Impact Analysis

If you are using the Tenda BE12 Pro router with firmware version 16.03.66.23, this vulnerability could have several severe impacts:

• Denial of Service (DoS): An attacker could crash the router, disrupting your network connectivity.
• Arbitrary Code Execution: An attacker could execute malicious code on the router, potentially taking full control of the device.
• Information Leakage: Sensitive data stored on or passing through the router could be exposed or stolen.
• Network Compromise: The router could be used as a pivot point to launch attacks against other devices on your network.
• Malware Installation: The attacker could install malware or backdoors on the router, allowing persistent access.

Since the attack can be launched remotely and does not require authentication, the risk of exploitation is significant if the router is exposed to the internet.

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Compliance Impact

This vulnerability could impact compliance with several common standards and regulations, depending on the context in which the affected router is used:

• GDPR (General Data Protection Regulation): If the router processes or transmits personal data of EU citizens, a breach resulting from this vulnerability could lead to unauthorized access or disclosure of personal data. This may violate GDPR requirements for data protection and could result in significant fines or legal action.
• HIPAA (Health Insurance Portability and Accountability Act): If the router is used in a healthcare setting and handles protected health information (PHI), exploitation of this vulnerability could lead to unauthorized access to PHI. This would violate HIPAA's security and privacy rules, potentially resulting in penalties.
• PCI DSS (Payment Card Industry Data Security Standard): If the router is part of a network processing payment card data, this vulnerability could compromise the security of cardholder data, violating PCI DSS requirements and leading to non-compliance penalties.
• ISO 27001: This standard requires organizations to implement controls to manage information security risks. Failure to address this vulnerability could indicate a lack of adequate security controls, potentially leading to non-compliance with ISO 27001.

In general, the vulnerability undermines the confidentiality, integrity, and availability of data, which are core principles of most compliance frameworks. Organizations using the affected router should assess the risk and take corrective actions to maintain compliance.

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Mitigation Strategies

To mitigate the CVE-2026-15696 vulnerability, follow these immediate steps:

• Upgrade the Tenda BE12 Pro router firmware to the latest version if a patch is available. Check the official Tenda website for updates: https://www.tenda.com.cn.
• If no patch is available, restrict access to the router's web interface by disabling remote administration and limiting access to trusted IP addresses only.
• Disable the `/goform/VirtualSer` endpoint if it is not required for normal operation. This can be done by modifying the router's configuration or firewall rules to block access to the endpoint.
• Monitor network traffic for suspicious activity targeting the `/goform/VirtualSer` endpoint. Use intrusion detection systems (IDS) or network monitoring tools to detect and block exploitation attempts.
• Replace the use of unsafe functions like `sprintf` with safer alternatives such as `snprintf` in custom firmware or scripts, if applicable. Implement strict input validation and sanitization for all user-controlled inputs.
• Apply the principle of least privilege by ensuring the router runs with minimal permissions and isolating it from critical network segments.

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