Attack Chain

1. The attacker identifies a vulnerable D-Link DI-8100 router running firmware version 16.07.26A1.
2. The attacker crafts a malicious HTTP request targeting the tgfile.htm CGI endpoint.
3. The malicious request includes an overly long string in the fn argument.
4. The router’s web server processes the request and passes the fn argument to the tgfile_htm function.
5. The tgfile_htm function fails to properly validate the length of the fn argument.
6. A buffer overflow occurs when the overly long fn argument is copied into a fixed-size buffer.
7. The buffer overflow overwrites adjacent memory, potentially including return addresses or other critical data.
8. The attacker gains arbitrary code execution on the router, potentially allowing them to take full control of the device.

Impact

Successful exploitation of this vulnerability allows an attacker to remotely execute arbitrary code on the D-Link DI-8100 router. This could lead to a complete compromise of the device, allowing the attacker to intercept network traffic, modify router settings, or use the router as a launchpad for further attacks against other devices on the network. Given the public availability of an exploit, widespread exploitation is possible, potentially affecting numerous home and small business networks.

Recommendation

• Monitor web server logs for abnormally long fn parameters in requests to /tgfile.htm using the provided Sigma rule to detect potential exploitation attempts.
• Implement rate limiting on HTTP requests to the router’s web interface to mitigate brute-force exploitation attempts.
• Since the source material only identifies a vulnerability, without a patch, consider replacing the affected device.