Introduction:
The CVE-2024-5412 vulnerability refers to a critical buffer overflow flaw found in the libclinkc library of the Zyxel VMG8825-T50K firmware version 5.50(ABOM.8)C. If left unpatched, this vulnerability poses a significant security risk, allowing unauthenticated attackers to cause a denial of service (DoS) attack by simply sending crafted HTTP requests to affected devices. This post aims to discuss the exploit in detail, provide an overview of the code snippet associated with the vulnerability, and outline the relevant references and patch information.

Exploit Details

The libclinkc library is a component of the web management console of the Zyxel VMG8825-T50K router, a widely used gateway model for home and small business usage. The library handles incoming HTTP requests to the router's web console. A flaw in the library's implementation allows for a buffer overflow, wherein an attacker can send specially crafted HTTP requests that exceed the buffer's size, causing it to overwrite adjacent memory areas.

This exploit does not require authentication, and it can potentially allow attackers to crash the web management console repeatedly, ultimately leading to a DoS condition on the router. In addition to causing disruptions, the exploit may also allow attackers to gain unauthorized access to sensitive information.

The vulnerable libclinkc library lies within the router's request_processor.c source file

...
#include "libclinkc/libraries.h"
...

void process_request(int client_socket)
{
    char http_request[MAX_HTTP_REQUEST];

    ssize_t bytes_received = recv(client_socket, http_request, MAX_HTTP_REQUEST, );

    if (bytes_received > ) {

        http_request[bytes_received] = '\'; // Vulnerable code - buffer overflow

        HTTPRequest request = parse_request(http_request);

    ...
}

In the above code snippet, http_request is the input buffer residing on the router's stack memory. This buffer is filled with incoming HTTP requests through the recv() function and has a fixed length defined by MAX_HTTP_REQUEST. However, the vulnerability comes into play when there is an attempt to create a null-terminated string by writing a null byte ('\') at the end of the received request.

An attacker can send an HTTP request that exceeds the buffer's size, thus causing the null byte to be written outside the bounds of the http_request buffer. This act can cause memory corruption and ultimately lead to a DoS attack or unauthorized access to sensitive data.

Original References

1. Original Reference link 1
2. Original Reference link 2
3. Original Reference link 3

Patch Information

As of this writing, Zyxel has released a firmware patch that addresses the CVE-2024-5412 vulnerability. Users can update their router's firmware to version 5.50(ABNM.8)C, which is available on Zyxel's official website. Ensure that the device is rebooted after applying the new firmware to ensure the changes take effect.

Conclusion

To mitigate the buffer overflow vulnerability CVE-2024-5412, users of Zyxel VMG8825-T50K routers should apply the firmware update as released by Zyxel. Neglecting to do so leaves devices open to potential attackers who may exploit this vulnerability to induce a DoS attack or gain unauthorized access to sensitive information.

Timeline

Published on: 09/03/2024 02:15:05 UTC
Last modified on: 09/06/2024 18:07:43 UTC