---

In early 2023, security researchers discovered and reported a privilege escalation vulnerability affecting millions of Windows devices. Assigned CVE-2023-21768, this flaw targets the Windows Ancillary Function Driver for WinSock (AFD.sys)—a core networking component, present since Windows NT! This post breaks down what happened, why it matters, and how attackers are (or could be) exploiting it, with code snippets and technical details, all in easy-to-understand language.

What is CVE-2023-21768?

CVE-2023-21768 is an *elevation of privilege* vulnerability in the Windows Ancillary Function Driver for WinSock (AFD.sys). It lets an attacker who already has code execution as a regular user gain SYSTEM privileges, as high as you can go on a Windows box.

Why is AFD.sys Important?

AFD.sys handles Windows low-level networking for applications. Since networking is everywhere, this service always runs in the background. If attackers find a bug here, they can affect almost every Windows user.

Affected Systems: Windows 7 through Windows 11 and the equivalent Windows Server editions

- Real-World Attacks? Yes, proof-of-concepts exist, and attackers are reportedly using it in targeted attacks.

How Does CVE-2023-21768 Work? (Technical Breakdown)

The vulnerability exists due to improper validation of user-supplied data in the way AFD.sys handles IOCTL (input/output control) requests. An attacker can craft a specific IOCTL request to AFD.sys, triggering a memory corruption or privilege escalation.

Key Part: IOCTL Code x120BB

Researchers found that by calling DeviceIoControl on the \\Device\Afd driver with a specific IOCTL code and specially crafted input, they could exploit the system’s poor handling of kernel pointers.

WARNING: For educational purposes only. Do not run on production systems.

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

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

    if (hDevice == INVALID_HANDLE_VALUE) {
        printf("[-] Failed to open AFD.sys device: %d\n", GetLastError());
        return 1;
    }

    DWORD IoctlCode = x120BB; // Vulnerable IOCTL
    BYTE InputBuffer[x30] = { /* Malicious data crafted here */ };
    DWORD BytesReturned;

    BOOL result = DeviceIoControl(
        hDevice,
        IoctlCode,
        InputBuffer,
        sizeof(InputBuffer),
        NULL,
        ,
        &BytesReturned,
        NULL
    );

    if (result) {
        printf("[+] IOCTL sent successfully.\n");
    } else {
        printf("[-] IOCTL failed: %d\n", GetLastError());
    }

    CloseHandle(hDevice);
    return ;
}

*Note*: The actual buffer content is omitted for obvious reasons. Security researchers typically need to reverse engineer the kernel code to craft a working exploit.

Real Exploit Scenario

Let’s say malware gains entry to a Windows laptop as a regular user (using phishing or a malicious document). Using an exploit for CVE-2023-21768, it can run code with SYSTEM privileges—disabling antivirus, stealing credentials, or adding new admin accounts.

How To Protect Yourself

- Patch Immediately: Microsoft issued a security update in February 2023. Here’s the official advisory.

Least Privilege: Minimize users running with admin rights.

- Security Software: Update and use behavioral-based antivirus products that can block exploitation attempts.

Further Reading & References

- Microsoft Advisory for CVE-2023-21768
- Project Zero write-up on Windows IOCTL vulnerabilities
- AFD.sys Overview
- Exploit DB PoC (if public)

Final Thoughts

CVE-2023-21768 is a reminder that even “old” core Windows drivers still carry risky code. If you’re responsible for Windows systems, patch and monitor now. If you’re a defender, watch for indicators of local privilege escalation. Attackers continue to hunt for these weaknesses every day.

Stay safe! 🛡️

*Author’s note: This post is exclusive content for the security community, written in plain language to help everyone understand complex threats.*

Timeline

Published on: 01/10/2023 22:15:00 UTC
Last modified on: 03/30/2023 20:15:00 UTC