CVE-2023-23420 - Inside the Windows Kernel Elevation of Privilege Vulnerability

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Cyber security is a cat-and-mouse game, and Windows, as the world’s most popular operating system, continues to be a prime target. In this long read, we’ll take a close look at CVE-2023-23420, a serious Windows Kernel Elevation of Privilege (EoP) vulnerability. We’ll break down how it works, walk through a proof-of-concept, review mitigation steps, and point to original sources for more learning.

What is CVE-2023-23420?

On February 14th, 2023, Microsoft patched a weakness tracked as CVE-2023-23420, labeled as a Windows Kernel Elevation of Privilege Vulnerability. If left unpatched, this bug could allow attackers to gain SYSTEM-level privileges—the highest on Windows—by running code in kernel mode. In simpler terms: anyone exploiting this vulnerability can take control of the whole device.

Microsoft’s official advisory: MSRC CVE-2023-23420

Where is the Vulnerability?

The issue exists in the Windows Kernel, specifically within the way it handles certain objects in memory. A local attacker (someone already on the machine) can trick the kernel into incorrectly managing memory, resulting in privilege escalation.

According to ZDI’s report, the bug relates to the handling of window objects, leading to a use-after-free condition—where a pointer is used after its memory is freed.

Creating window objects with special styles or properties.

2. Triggering a situation where a window object’s memory is freed but a pointer to it is still referenced.
3. Causing the system to use the dangling pointer, potentially leading to arbitrary code execution in the privileged kernel context.

The exploit is not remote—the attacker already needs local access. However, privilege escalation bugs are a favorite for malware and ransomware makers seeking to gain full control from a lower-privileged entry point.

Example Proof-of-Concept (PoC)

While Microsoft and others have not released a full PoC, security researchers have shared similar exploits for use-after-free EoP bugs in the Windows kernel for educational purposes. Here’s a simple illustration (not a full exploit):

// Pseudo-code: Simulating window object Use-After-Free
HWND hwnd = CreateWindowEx(...);
// ... manipulate hwnd to set properties/triggers
DestroyWindow(hwnd); // Free the window object

// There is a kernel pointer still referring to hwnd here (bug)!
SomeKernelFunction(hwnd); // This call now operates on freed memory

The attacker would need to carefully spray memory so that, after DestroyWindow, the freed chunk is replaced with attacker-controlled data. When the kernel function, acting on the dangling pointer, accesses this memory, the attacker can hijack execution flow.

If you want to see a real exploit for a similar class of bug, check out Ivan Fratric’s detailed example.

Real-World Impact

Successful exploitation leads to complete machine compromise. Once SYSTEM-level access is achieved, an attacker can:

Modern EDR tools may detect exploit patterns and privilege escalation attempts.

Read Microsoft’s detailed guidance here:
https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2023-23420

Final Thoughts

CVE-2023-23420 is a perfect example of how a seemingly small bug in kernel memory handling can have massive consequences. If you’re responsible for Windows machines, update them as soon as possible. If you’re a security enthusiast, keep digging—kernel EoP vulnerabilities are still one of the richest areas for learning (and securing our digital world).

Timeline

Published on: 03/14/2023 17:15:00 UTC
Last modified on: 03/20/2023 03:55:00 UTC