This issue has been resolved. Please refer to the topmost comment.

---------------------------------------------------------------------------------------------------------------------------------------------------

System: Windows Vista x64 (Version 6.0, Build 6002: SP2)
Device: Dell Latitude E6500 (shipped with a Windows Vista Business x86 OEM Key)
Date of Installation: Saturday 13th, March 2021 (Yesterday as of writing this)

Hello, MSFN community.
Ever since I installed a fresh, genuine, unmodified copy of Windows Vista Ultimate x64 SP2 on my system yesterday, I've been having issues getting Windows Update to run. It instead fires Error Code 80072EFE. Now, I've done some research and the results I've found were to run a rootkit checker (nothing detected, even after installing an additional driver), pausing my antivirus (Avast Free), updating the Windows Update client, installing an update that supposedly enables SHA-2 signing (the article I got that from was from 2019, doubt it still works), removing or renaming the Catroot2 folder, resetting my hosts file and registering the following DLL files:

atl.dll (Success)
urlmon.dll (Success)
Shdocvw.dll (Dll loaded but entry-point DllRegisterServer not found)
Actxprxy.dll (Success)
Oleaut32.dll (Success)
Mshtml.dll (Loaded but entry-point DllRegisterServer not found)
Browseui.dll (Loaded but entry-point DllRegisterServer not found)
actxprxy.dll (Success)
softpub.dll (Success)
wintrust.dll (Success)
initpki.dll (Module "initpki.dll failed to load; see full error in attachments)
dssenh.dll (Success)
CRYPTDLG.DLL (Success)

Furthermore, I had successfully installed the following updates manually as an attempted solution:

KB3145739 (Security Update for Microsoft Windows)
KB971512 (Update for Microsoft Windows)
KB4039648 (Update for Microsoft Windows)
KB970158 (Kernel-Mode Driver Framework v1.9)
KB955430 (Update for Microsoft Windows)
KB938371 (Update for Microsoft Windows)
KB937287 (Update for Microsoft Windows)
KB935509 (Update for Microsoft Windows)

None of these supposed solutions had worked for me, though (although some supposedly did for some users). Is there anything else I could attempt at this point to have Windows Update running properly (and to, ideally, also get SHA-2 code signing support)?

My goal is to get Windows Vista onto the latest version available and to then install the Extended Kernel.

Sincerely,
MaxB

P.S.: In case there is no solution, I have already downloaded all Vista updates through Windows Patch Loader. However, Windows Patch Loader outputs all updates as Cabinet Files (except the service packs, which are already installed). Installing these manually via the command line would be a pain to do. Is there a way to speed that up, or to avoid having to use the command line for this case entirely (getting the updates as MSU packages instead, for example)?

EDIT: Clicking the "Find out more" link on the update panel gives me the "Internet Explorer cannot display the website" error (IE7). Opening the link through a newer browser (Pale Moon 27.9.4) brings me to a newer version of the webpage, which only gives me directions on how to navigate to the Update panel in Windows 7.

 

Edited March 15, 20215 yr by MaxB
Issue resolved.

This issue has been solved successfully. This is the solution.

I had firstly reinstalled Vista Ultimate x64 using an ISO which contained the Extended Kernel pre-installed.

This I followed up by installing the (prerequisites for the) Windows Update Client fix (Patch WUC as Vista) and restarting my PC (every time the guide told me to).

Afterwards, I manually installed every update from the linked folder (excluding the Windows Update Agent, the KB890830 executable update, which is the malicious software removal tool, as well as the IE9 and MP11 updates. And, of course, the service packs, as those were pre-loaded) and restarted my PC:
Once I had done all that, the Windows Update Client was available for use again.