In June 2024, Microsoft disclosed CVE-2024-30087, a critical zero-day vulnerability within Win32k, the Windows kernel mode device driver. This flaw allows a local attacker to escalate their privileges, obtaining SYSTEM-level access from a restricted account. In simpler words: a regular user (or malware running as a low-privileged user) can take complete control of the machine.

Below, we’ll break down what the vulnerability is, how it can be exploited, and show a proof of concept (PoC) code snippet for research and education purposes.

What is Win32k and Why Does it Matter?

Win32k.sys is a part of the Windows kernel that handles the graphical subsystem, interacting tightly with user-mode processes. Over the years, it’s been a favorite target for attackers because it runs with high privileges and contains complex code exposed to user input.

Vulnerabilities here, like CVE-2024-30087, often let attackers jump from a limited user all the way up to administrator or SYSTEM, bypassing many protections.

Microsoft’s Description

> “An elevation of privilege vulnerability exists when the Windows Kernel (Win32k) improperly handles objects in memory. An attacker who successfully exploited this vulnerability could run arbitrary code in kernel mode and take complete control of the system.”

Original Microsoft advisory: MSRC CVE-2024-30087

Technical Details

When certain graphical operations are triggered, Win32k does not correctly validate memory pointers or object states, allowing for a Use-After-Free (UAF) scenario. Specifically, by manipulating window objects or certain GDI functions, an attacker can cause the kernel to operate on memory that has been freed and reclaimed by attacker-controlled data.

This results in high-impact exploits: attackers can install programs, view/change/delete data, or create new accounts with full admin rights.

Here’s a simplified version of how attackers approach CVE-2024-30087

1. Craft Malicious Window Objects: The attacker creates or manipulates window objects using user-mode code such as CreateWindowEx() or similar GDI calls.
2. Trigger UAF: By destroying or mismanaging these objects, they force the kernel to perform operations on freed memory.
3. Gain Control: The freed memory is filled with attacker-controlled data, so when Win32k calls into the freed object, arbitrary code execution or privilege escalation occurs.
4. Escalate Privileges: With code running in kernel mode, the attacker replaces their access token with that of SYSTEM.

Proof-of-Concept Demo (Educational Only)

Below is a *simplified* PoC to show how a normal process might interact with vulnerable kernel memory. Note this is not a weaponized exploit, but still do not run on production systems.

// CVE-2024-30087 Proof-of-Concept Demo (For Educational Purposes Only)
#include <windows.h>
#include <stdio.h>

int main() {
    // Step 1: Create a window object
    WNDCLASS wc = {};
    wc.lpfnWndProc = DefWindowProc;
    wc.hInstance = GetModuleHandle(NULL);
    wc.lpszClassName = "VulnWindow";
    RegisterClass(&wc);

    HWND hwnd = CreateWindowEx(, "VulnWindow", "Test", WS_OVERLAPPEDWINDOW,
                               CW_USEDEFAULT, CW_USEDEFAULT, 500, 500,
                               NULL, NULL, wc.hInstance, NULL);

    // Step 2: Trigger race condition/use-after-free in win32k
    // (Real exploit would manipulate internal kernel state here)
    // This is a dummy demonstration:
    DestroyWindow(hwnd);

    // Step 3: Attacker allocates memory and hopes win32k uses it
    // In a full exploit, heap spraying or other methods would be used

    printf("If this were weaponized, privileges may be escalated here.\n");
    return ;
}

*Note: This code is for concept illustration only. Actual exploits are highly complex, often dozens of pages long and require deep kernel knowledge.*

References & Further Reading

- Microsoft Security Response Center: CVE-2024-30087
- Google Project Zero: Kernel Exploitation Basics
- Win32k Internals — hex-rays.com
- HackerOne Writeup on Win32k Bugs

Mitigation

Patch your systems! As soon as Microsoft released updates, hotfixes became available via Windows Update. If you can’t update right away, minimize risky activities, avoid running unknown code, and restrict access to administrative accounts.

Conclusion

CVE-2024-30087 is a classic example of how a mistake deep in the Windows kernel—especially in Win32k—can give attackers a highway to privilege escalation. By understanding these flaws, both defenders and researchers can help improve software security for everyone.

Stay safe, keep your systems patched, and always be cautious with untrusted code!

Timeline

Published on: 06/11/2024 17:15:56 UTC
Last modified on: 07/19/2024 21:13:32 UTC