Executive Summary

This vulnerability exists in the D-Link DI-8100 router firmware, specifically in the tgfile.htm CGI endpoint within the tgfile_htm function. It is caused by unsafe use of the sprintf function with user-supplied input through the "fn" parameter. The function uses a fixed-size stack buffer of 128 bytes and prepends a fixed string before appending the user input without checking its length. If the "fn" parameter exceeds 117 bytes, it causes a stack-based buffer overflow by writing beyond the buffer boundary.

This overflow can corrupt the stack frame and potentially overwrite the saved return address, leading to control-flow hijacking when the function returns. An attacker can exploit this remotely by sending a crafted HTTP request with an overly long "fn" parameter, which can crash the web server process or possibly allow remote code execution.

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Impact Analysis

The vulnerability can have several serious impacts:

• Denial of Service (DoS): The web server process crashes when exploited, causing the administrative interface to become unresponsive until the device is rebooted.
• Potential Remote Code Execution (RCE): Due to control-flow hijacking, an attacker might execute arbitrary code remotely, compromising the device.
• Integrity Risk: The attacker can manipulate the device's operation by exploiting the buffer overflow.
• Confidentiality Risk: There is a low risk of stack memory leakage, which might expose sensitive information.

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Detection Guidance

This vulnerability can be detected by sending a crafted HTTP request to the tgfile.htm CGI endpoint with an overly long "fn" parameter. A proof-of-concept uses a curl command to send a request with a 200-character "fn" parameter, which causes the web server to crash and become unresponsive.

• Use the following curl command to test for the vulnerability: curl "http://<target-ip>/tgfile.htm?fn=$(python3 -c 'print("A"*200)')"

If the web server crashes or the administrative interface becomes unresponsive after this request, the device is likely vulnerable.

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Mitigation Strategies

Immediate mitigation steps include avoiding exposure of the vulnerable CGI endpoint to untrusted networks and restricting access to the device's administrative interface.

If possible, reboot the device after detecting a crash caused by exploitation attempts to restore service temporarily.

Monitor network traffic for suspicious requests targeting the tgfile.htm endpoint with unusually long "fn" parameters.

Since the exploit is public and can cause denial of service or potentially remote code execution, consider isolating the device from critical networks until a firmware update or patch is available.

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Compliance Impact

The vulnerability in the D-Link DI-8100 router allows remote attackers to cause a buffer overflow via the tgfile.htm CGI endpoint, potentially leading to remote code execution and denial of service. This can compromise the integrity and availability of the device.

Such impacts on integrity and availability could affect compliance with standards like GDPR and HIPAA, which require protection of data confidentiality, integrity, and availability. Specifically, the potential for remote code execution and service disruption could lead to unauthorized access or loss of sensitive data, violating these regulations.

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

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