CVE-2023-43867 - Critical Vulnerability in D-Link DIR-619L B1 2.02: Buffer Overflow within formSetWanL2TP Function Expounded

A critical vulnerability, dubbed CVE-2023-43867, has recently been discovered in D-Link's DIR-619L B1 router with firmware version 2.02. This vulnerability exposes the router to a buffer overflow attack that can be executed via the 'formSetWanL2TP' function. An attacker can exploit this vulnerability to execute arbitrary code remotely and gain unauthorized access to the router's control panel. In this post, we will delve into the details of this vulnerability and explain how it can be exploited by potential adversaries.

Vulnerability Details

A buffer overflow occurs when a program writes more data to a fixed-length buffer than it can accommodate. If an attacker can control the overflowed data, they can overwrite adjacent memory locations and potentially change the flow of the program's execution by overwriting important memory values such as return addresses or function pointers. The vulnerability in the formSetWanL2TP function allows an attacker to send specially crafted input that causes a buffer overflow, thereby allowing the attacker to execute arbitrary code.

The buffer overflow vulnerability CVE-2023-43867 is present in the D-Link DIR-619L B1 2.02 router within the 'formSetWanL2TP' function. This function is responsible for processing and setting the router's L2TP WAN settings. An attacker can send crafted HTTP POST data to this function, which results in a stack-based buffer overflow. This can then be misused to execute arbitrary code on the device.

The following code snippet demonstrates the vulnerable part of the 'formSetWanL2TP' function

void formSetWanL2TP(request *req)
{
   ...
   char buf[512];
   ...
   strcpy(buf, req->postData);
   ...
}

In the code snippet above, the 'strcpy()' function is used to copy the incoming POST data (req->postData) into a fixed-length buffer 'buf' with a size of 512 bytes. As 'strcpy()' does not check for the destination buffer's size, it's prone to buffer overflow if the length of the POST data exceeds the size of the buffer.

Exploit Details

To exploit this vulnerability, an attacker would need to prepare and send a malicious HTTP POST request to the vulnerable router. The request would contain crafted data specifically designed to overflow 'buf' within the 'formSetWanL2TP' function. This crafted data would contain a NOP (No Operation) sled, followed by the attacker's desired shellcode to be executed on the router. The ultimate goal would be to overwrite the return address or a function pointer, forcing the execution flow to jump to the attacker's shellcode.

Original References

For a thorough understanding of the CVE-2023-43867 vulnerability, kindly refer to the following sources:

1. CVE Details
2. Exploit Database

Mitigation

As of now, there is no official firmware update from D-Link that addresses this critical vulnerability. However, users can temporarily secure their routers by disabling remote administration access and ensuring that they use strong credentials for all user accounts. Additionally, users are advised to keep monitoring the D-Link official website for updates and firmware patches related to this vulnerability.

Conclusion

In conclusion, CVE-2023-43867 poses a severe security risk to users operating D-Link DIR-619L B1 routers with firmware version 2.02. The buffer overflow vulnerability in the 'formSetWanL2TP' function can be exploited remotely by attackers to gain unauthorized access to the router's control panel and execute arbitrary code. Disabling remote administration access and employing strong user credentials are temporary mitigation measures until an official firmware update is available. Always be vigilant and up-to-date with the latest security information to ensure adequate protection against potential threats.

Timeline

Published on: 09/28/2023 14:15:22 UTC
Last modified on: 09/29/2023 04:32:42 UTC