Executive Summary

CVE-2026-7857 is a stack-based buffer overflow vulnerability found in the D-Link DI-8100 device running firmware version 16.07.26A1. It occurs in the web management interface's CGI handler at the /user_group.asp endpoint. The vulnerability arises because the function uses the unsafe sprintf function to concatenate user-supplied parameters into a fixed-size stack buffer without proper bounds checking.

An authenticated attacker can exploit this by sending a crafted HTTP POST request with an excessively long string in the 'attr' parameter, causing the buffer to overflow, corrupting the stack, and potentially crashing the HTTP service.

In some cases, this overflow could lead to remote code execution depending on the memory layout and payload used.

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Impact Analysis

This vulnerability can impact you by allowing an authenticated attacker to cause a Denial of Service (DoS) by crashing the HTTP service of the device, making the web management interface unavailable.

Additionally, depending on the memory layout and the crafted payload, the attacker might achieve remote code execution, which could allow them to take control of the device or execute arbitrary code.

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Detection Guidance

This vulnerability can be detected by monitoring for abnormal behavior or crashes in the HTTP service of the D-Link DI-8100 device, especially when accessing the /user_group.asp endpoint.

A practical detection method involves sending a crafted HTTP POST request to the /user_group.asp endpoint with an excessively long string in the 'attr' parameter to test for buffer overflow symptoms such as connection resets or service crashes.

For example, using curl to send a test payload:

• curl -X POST http://<device-ip>/user_group.asp -d "name=test&mem=1&pri=1&attr=$(python3 -c 'print("A"*1000)')"

If the HTTP service crashes or the connection is reset, it indicates the presence of the vulnerability.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable /user_group.asp endpoint to trusted and authenticated users only, as the attack requires authentication.

Additionally, monitor the device for any unusual HTTP service crashes or resets that may indicate exploitation attempts.

If possible, apply firmware updates or patches from the vendor that replace the unsafe sprintf function with a safer alternative like snprintf to prevent buffer overflow.

As a temporary measure, consider disabling remote management or limiting management access to a secure network segment until a patch is available.

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Compliance Impact

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

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