D-Link DI-8100 Stack-Based Buffer Overflow Vulnerability

A stack-based buffer overflow vulnerability has been identified in D-Link DI-8100 routers running firmware version 16.07.26A1. The vulnerability resides within the sprintf function of the yyxz.asp file. Successful exploitation allows remote attackers to execute arbitrary code. Publicly available exploit code exists, increasing the risk of widespread exploitation targeting these devices. Given the potential for complete system compromise, this poses a significant risk to affected D-Link router users.

Attack Chain

1. Attacker sends a malicious HTTP request to the vulnerable D-Link DI-8100 device.
2. The request targets the yyxz.asp file.
3. The ID argument in the request is manipulated to contain an overly long string.
4. The sprintf function in yyxz.asp is called with the attacker-controlled ID as input.
5. Due to the lack of proper bounds checking, the overly long ID overflows the stack buffer.
6. The attacker overwrites adjacent memory on the stack, including the return address.
7. Upon function return, control is transferred to the attacker-controlled address.
8. The attacker executes arbitrary code on the device.

Impact

Successful exploitation of this vulnerability allows a remote attacker to execute arbitrary code on the affected D-Link DI-8100 router. This could lead to complete compromise of the device, allowing attackers to intercept network traffic, modify router settings, or use the device as a bot in a botnet. Given that this device is typically deployed on the network perimeter, a successful attack could compromise the internal network.

Recommendation

• Apply available patches or firmware updates from D-Link to remediate the sprintf stack-based buffer overflow vulnerability (CVE-2026-7851).
• Monitor web server logs for suspicious requests targeting the yyxz.asp file with unusually long ID parameters, indicative of potential exploitation attempts.
• Deploy the Sigma rules provided to detect exploitation attempts in network traffic.