CVE-2024-21405: Unraveling the Microsoft Message Queuing (MSMQ) Elevation of Privilege Vulnerability

In this deep dive, we'll take a closer look at the Microsoft Message Queuing (MSMQ) Elevation of Privilege Vulnerability (CVE-2024-21405). This vulnerability affects versions of Windows Server and can be exploited by an attacker to gain higher privileges on the system. As we analyze the details of the exploit, we'll include code snippets, original references, and additional resources for those interested in learning more.

Background on MSMQ

MSMQ, or Message Queuing, is a Windows system service that allows applications to communicate asynchronously—that is, without explicit synchronization or waiting for a response. Sending and receiving messages can be performed locally or remotely, through queues, making it a versatile tool for communication between different systems and services. You can find more information on MSMQ in the official Microsoft documentation [1].

Vulnerability details

The CVE-2024-21405 vulnerability stems from improper handling of symbolic links in the MSMQ service. This can be exploited by a malicious actor to create a symlink that points to an arbitrary file. When a legitimate operation occurs within the MSMQ service, the attacker-controlled link can cause unauthorized access, allowing the attacker to elevate their privileges on the system.

This vulnerability's severity is high, as it impacts a wide range of supported Windows Server versions and can potentially give an attacker full control over the system.

Here's a simplified code snippet demonstrating how this vulnerability might be exploited

#include <iostream>
#include <Windows.h>

bool exploitMSMQ()
{
    /* Attacker-controlled parameters */
    WCHAR target_path[] = L"\\??\\C:\\Windows\\System32\\target.file";
    WCHAR payload_path[] = L"\\??\\C:\\attacker\\controlled\\payload.txt";

    ...
    
    /* Create a symlink to the target file */
    BOOL result = CreateSymbolicLink(symLinkPath, target_path, );
    
    if (!result) {
        std::cout << "Could not create the symbolic link" << std::endl;
        return false;
    }

    ...
 
    /* Perform the MSMQ operation */
    HWND handle_MSMQ = OpenMSMQ();
    
    ...
    
    /* Perform the operation that triggers the vulnerability */
    result = SendMessage(handle_MSMQ, payload_path, strlen(payload_path));

    if (result == -1) {
        std::cout << "Error sending the message." << std::endl;
        return false;
    }
    
    return true;
}

This example demonstrates how an attacker could exploit the vulnerability by creating a symbolic link to a target file and then triggering the vulnerable operation within MSMQ. The code is an example only and not a functioning exploit. It is provided here for educational purposes and to give a sense of how this vulnerability might appear in practice.

Mitigation and remediation

To mitigate the risk of this vulnerability, Microsoft has released a patch for supported versions of Windows Server. You can find details about the patch, as well as links to download it, in Microsoft's Security Update Guide [2]. It's crucial to install security updates promptly to minimize the risk of exploiting known vulnerabilities in your systems.

Conclusion

CVE-2024-21405 is a high-severity vulnerability actively affecting Windows Servers, in which an attacker can exploit improper handling of symbolic links in the MSMQ service, resulting in unauthorized access and elevated privileges. By understanding this flaw, and others like it, we can work to improve the security of our systems and better protect against these types of vulnerabilities. Be sure to keep your systems patched and up-to-date to minimize the risk of exploitation.

References

[1] Microsoft Message Queuing (MSMQ)
https://docs.microsoft.com/en-us/previous-versions/msp-n-p/ms811035(v=pandp.10)

[2] Security Update Guide – CVE-2024-21405
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2024-21405

Timeline

Published on: 02/13/2024 18:15:59 UTC
Last modified on: 02/22/2024 17:57:19 UTC