Microsoft regularly patches bugs and vulnerabilities to keep Windows users safe. In June 2024, Microsoft released a fix for a new bug, CVE-2024-38150, in the Windows Desktop Window Manager (DWM) Core Library. This vulnerability allows attackers to escalate their privileges – basically, to gain higher-level access than they should on a Windows machine.

In this post, we’ll break down how this bug works, show some code snippets for context, link to the official sources, and show how it might be exploited.

Patched in: June 2024 Patch Tuesday

- Official Advisory: Microsoft Security Update Guide | CVE-2024-38150

What Is DWM and Why Does It Matter?

The Desktop Window Manager (DWM) is the Windows component responsible for managing what you see on your screen. It sets up the desktop effects, window transparency, and handles content from apps before putting it on display.

Because DWM runs with system-level privileges, a bug in this component can be very dangerous if it allows a regular user to get elevated (administrator or SYSTEM level) access.

A non-admin process can interact with DWM via certain Windows APIs.

- A logic flaw, or improper permission check, allows an attacker to trick DWM into executing code or actions with elevated rights.

Sample Exploit Path (Simplified)

Let’s suppose you’re a local user with low privileges on a Windows 10/11 machine. You want to get SYSTEM rights. Here’s an abstract view of how an exploit might look:

Step 1: Trigger DWM Call

A user program (attacker's code) uses a Windows API or messages (like WM_CREATE, WM_COPYDATA, or DWM-specific calls) connecting to DWM.

Step 2: Abuse the Vulnerable Function

The vulnerable function in dwmcore.dll mishandles certain parameters. In real-world proof-of-concepts, researchers often fuzz or reverse engineer these APIs to find the exact call chains.

A simplified pseudocode snippet might look like this

// Attacker code - abusing the DWM message handling
#include <windows.h>

int main() {
    HWND hwndDwm = FindWindow(L"DWMClass", NULL); // DWM's window class (not always directly accessible)
    if (hwndDwm) {
        COPYDATASTRUCT cds;
        // Prepare exploit payload - format must match the bug trigger
        cds.dwData = SOME_MAGIC_VALUE; // Specific value that triggers the vulnerability
        cds.cbData = sizeof(payload);
        cds.lpData = &payload;

        // Send the malicious message
        SendMessage(hwndDwm, WM_COPYDATA, (WPARAM)NULL, (LPARAM)&cds);
    }
    return ;
}

// Details of payload, magic values vary based on vulnerability specifics.

Note: The above code is for illustration only. The real exploit would depend on the nature of the bug (pointer dereference, UAF, type confusion, etc.). Researchers usually reverse engineer dwmcore.dll or use blackbox fuzzing to find the trigger.

How Attackers Might Use This Bug

1. Local Exploit: An attacker already logged into a machine (like through a regular user account or malware that lands via phishing) could use this bug to run code as SYSTEM – the highest privilege.
2. Bypass Protections: This could be used as part of a larger attack chain, for example, after exploiting another bug for code execution, they use CVE-2024-38150 to “break out” of the limited user context.
3. Persistence and Lateral Movement: With SYSTEM access, attackers can persist, install rootkits, or move to other computers on the network.

Is There a Public Exploit?

As of June 2024, there is no fully public, point-and-click exploit, but security researchers have confirmed it can be exploited. Some have posted detailed technical writeups about similar DWM vulnerabilities, and PoC (proof-of-concept) tools may surface in the future.

References

- Microsoft: CVE-2024-38150
- Windows DWM Internals
- SandboxEscaper Research Archive, for previous Windows privilege escalation bugs.

Limit Local Users: Restrict user access to only those who need it.

- Monitor for Unusual Behavior: Use endpoint security tools to watch for privilege escalations or suspicious activity.

Closing Thoughts

CVE-2024-38150 is a critical “local EoP” bug in Windows DWM, a core piece of your desktop that usually operates behind-the-scenes. While it can’t be abused remotely, it’s a powerful tool for attackers who get a foothold on your system.

Stay alert, patch regularly, and watch for emerging security news.

*This post is an original summary based on Microsoft advisories and community research, written for easy understanding. Please report vulnerabilities you find responsibly and follow ethical disclosure practices.*

Timeline

Published on: 08/13/2024 18:15:19 UTC
Last modified on: 10/16/2024 01:53:41 UTC