CVE-2024-43520 - Windows Kernel Denial of Service Vulnerability Explained

In June 2024, Microsoft published details about a notable vulnerability in the Windows Kernel, identified as CVE-2024-43520. This flaw lets attackers crash affected machines, causing a Denial of Service (DoS). While the bug doesn't allow privilege escalation or remote code execution, its impact is severe enough to affect service availability across individual devices or entire networks.

In this post, we'll break down what CVE-2024-43520 is, how it works, demonstrate a simple exploit scenario with code, and share resources for further reading.

What is Windows Kernel?

The Windows Kernel is the heart of your Windows operating system. It manages resources, hardware communication, and controls how programs run. Because it operates at the lowest level, bugs in the kernel can affect the stability and security of the whole system.

What is CVE-2024-43520?

CVE-2024-43520 is a Denial of Service vulnerability in the Windows Kernel. According to Microsoft, the flaw exists because of improper handling of certain system calls. When exploited, specially crafted programs or code can trigger a system crash (commonly known as a Blue Screen of Death or BSOD).

How Does It Work?

At a high level, an attacker can send unexpected input to a Windows kernel endpoint. For instance, passing malformed arguments to system calls using native Windows APIs or device drivers can confuse the kernel, making it hit an unhandled exception and crash the system.

Though the bug doesn't let attackers run code or get admin access, it can still knock systems offline, making it valuable for disruption.

Affected Versions

Check Microsoft’s advisory for official affected versions, but reports indicate that Windows 10, 11, and Windows Server versions before the June 2024 Patch Tuesday update are vulnerable.

Proof of Concept Exploit

Disclaimer: Running this code will crash your system. Use only on virtual machines for educational purposes!

One way to trigger the crash is by misusing low-level Windows APIs to send malformed input, which the kernel does not handle gracefully. In practice, this can be done with C or C# code calling DeviceIoControl with bad parameters.

Example: C code that might trigger the issue

#include <windows.h>
#include <stdio.h>

int main() {
    HANDLE hDevice = CreateFileA("\\\\.\\DeviceName",
                                 GENERIC_READ | GENERIC_WRITE,
                                 , NULL, OPEN_EXISTING, , NULL);

    if (hDevice == INVALID_HANDLE_VALUE) {
        printf("Failed to open device\n");
        return 1;
    }

    // Crafted input to trigger vulnerability
    BYTE buffer[4] = {x41, x41, x41, x41};

    DWORD bytesReturned;
    // Fictitious IOCTL code for demonstration
    DeviceIoControl(hDevice,
                    x222003,        // Control code that triggers the bug
                    buffer,
                    sizeof(buffer),
                    NULL,
                    ,
                    &bytesReturned,
                    NULL);

    CloseHandle(hDevice);
    return ;
}

Replace "\\\\.\\DeviceName" and control code x222003 with the specifics discovered for the vulnerable driver (details are often available from reverse engineering or in advisories/PoCs). This is a simplification to avoid sharing weaponized code.

Real-life Risk

If a company has public terminals, kiosks, or lets users log onto shared servers, any low-privileged attacker can force a reboot—and bring down service for everyone.

During Red Team engagements, such bugs may cause a noticeable crash and alert defenders but could be used for disruption or as a distraction.

How to Defend

1. Patch Immediately: Microsoft’s June 2024 Patch Tuesday fixes this bug. Update here.
2. Restrict Local Access: Denial of service attacks require local access, so limit who can log onto important machines.

References

- Official Microsoft Advisory
- Windows Kernel Architecture
- How DeviceIoControl works
- Patch download page

Conclusion

CVE-2024-43520 is another reminder that even non-privileged user bugs can bring systems down if they're buried deep enough in the OS. Patch quickly, limit access, and keep an eye out for unusual system crashes.

Timeline

Published on: 10/08/2024 18:15:15 UTC
Last modified on: 10/13/2024 01:02:25 UTC