Executive Summary

CVE-2026-35717 is a stack-based buffer overflow vulnerability found in the export_language.cgi binary of the VIVOTEK FD8136 camera firmware version FD8136-VVTK-0300a.

This vulnerability occurs at the /cgi-bin/admin/export_language.cgi endpoint, which requires authentication. The binary reads the Content-Length value from a POST request and uses it directly as the size to read data into a fixed-size 0x60-byte stack buffer without proper bounds checking.

Because the binary lacks stack canaries or other memory protections, an attacker can send a crafted POST request with a body larger than 0x60 bytes, causing a buffer overflow that overwrites the saved link register.

This overflow allows the attacker to redirect execution flow to shellcode placed in the request memory, enabling arbitrary code execution with root privileges.

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Impact Analysis

This vulnerability allows an authenticated remote attacker to execute arbitrary code as the root user on the affected VIVOTEK FD8136 device.

Exploitation can lead to full system compromise, including unauthorized control over the device, potential data theft, disruption of surveillance functions, and use of the device as a foothold for further network attacks.

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Detection Guidance

This vulnerability can be detected by monitoring for unusual or crafted POST requests to the /cgi-bin/admin/export_language.cgi endpoint on VIVOTEK FD8136 devices running firmware FD8136-VVTK-0300a.

Specifically, detection involves checking for POST requests with a Content-Length header value exceeding 0x60 bytes, which is the size of the vulnerable stack buffer.

Commands to detect such activity could include using network traffic analysis tools like tcpdump or Wireshark to filter HTTP POST requests to the vulnerable endpoint.

• tcpdump -i <interface> 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' -A | grep '/cgi-bin/admin/export_language.cgi'
• Use curl or similar tools to test the endpoint with controlled POST requests to verify if the device responds abnormally.

Additionally, reviewing device logs for authentication followed by POST requests to this endpoint with large Content-Length values may help identify exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the /cgi-bin/admin/export_language.cgi endpoint to trusted users only, as the vulnerability requires authentication.

Implement network-level controls such as firewall rules or access control lists to limit which IP addresses can reach the vulnerable endpoint.

Monitor and block POST requests with unusually large Content-Length headers targeting this endpoint.

If possible, update the device firmware to a version where this vulnerability is patched or contact VIVOTEK support for official remediation guidance.

Until a patch is available, consider disabling or restricting the export_language.cgi functionality if it is not essential.

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Compliance Impact

The vulnerability allows authenticated remote attackers to execute arbitrary code as root on the affected VIVOTEK FD8136 device. This could lead to unauthorized access, data breaches, or manipulation of sensitive information stored or processed by the device.

Such unauthorized access and potential data compromise could negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of personal and sensitive data against unauthorized access and breaches.

However, the provided information does not explicitly detail the direct compliance implications or specific regulatory impacts of this vulnerability.

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