Windows Vista build 5000 (vbl_core.040808-2000)

6.0.5000.vbl_core.040808-2000
	Build of Windows Vista
OS family	Windows NT
Version number	6.0
Build number	5000
Architecture	x86
Build lab	vbl_core
Compiled on	2004-08-08
Expiration date
Timebomb	2005-08-03 (+360 days)
SKUs
	Professional
Product key
	TCP8W-T8PQJ-WWRRH-QH76C-99FBW
About dialog

Windows Vista build 5000 (vbl_core.040808-2000) is a build of Windows Vista. On 23 January 2020, this build was listed on a thread by UX.Unleaked blog founder Grabberslasher to be released to the BetaArchive FTP, and was released in the third set of his 33 Longhorn/Vista builds on 26 January 2020, alongside build 4048, other compiles of this build, and build 5001.^[1]

This build by default has a severe bug where it appears to hang as soon as Windows switches to graphical mode, ending up with a solid blue or black screen, making this build not installable under normal conditions.

Bug analysis[edit | edit source]

Module name: win32k.sys

Reason: An uninitialised variable which causes win32k to raise Access Violation exception (by reading null pointer) and failing without any notice.

When Windows loads, it only shows a blank blue or black background without any cursor or watermark. Keyboard interrupts are also stuck/unregistered. First checks show that kernel idle loop is running fine and processing interrupts. There are no exceptions or bugchecks logged into WinDbg, hence the next check is to set breakpoints on nt!ExRaiseStatus and nt!ExRaiseAccessViolation, which apparently is what win32k is calling and leaving the function it is in. According to the following stack, it is either being called at win32k!EngFreeModule+0x5c9 (the preceding instruction), or the called function has called it:

f75d6d24 nt!ExRaiseAccessViolation
f75d6d48 win32k!EngFreeModule+0x5ce
f75d6d50 win32k!EngFreeModule+0x4b5
f75d6da0 nt!KeReleaseInStackQueuedSpinLockFromDpcLevel+0xb14
f75d6da4 ntdll+0x18c3c
f75d6da8 0x75a69626

Checking the code, it is calling the function located at win32k!EngMulDiv+0x29c0:

win32k!EngFreeModule+0x5b1:
bf8a0581 e84a5effff      call    win32k!EngMultiByteToUnicodeN+0x4310 (bf8963d0)
bf8a0586 893530079cbf    mov     dword ptr [win32k!HT_Get8BPPMaskPalette+0x30bb0 (bf9c0730)],esi
bf8a058c 8935cc219cbf    mov     dword ptr [win32k!HT_Get8BPPMaskPalette+0x3264c (bf9c21cc)],esi
bf8a0592 ff1500119abf    call    dword ptr [win32k!HT_Get8BPPMaskPalette+0x11580 (bf9a1100)]
bf8a0598 50              push    eax
bf8a0599 e8e280f8ff      call    win32k!EngMulDiv+0x29c0 (bf828680)
bf8a059e 8bd8            mov     ebx,eax   <-- The return address in the stack, second frame (win32k!EngFreeModule+0x5ce)
bf8a05a0 3bdf            cmp     ebx,edi

Inside that procedure, using a line-by-line tracing where it ends up calling ExRaiseAccessViolation has been found in the following part:

win32k!EngMulDiv+0x2b62:
=== bf828822 3b0d9c219cbf    cmp     ecx,dword ptr [win32k!HT_Get8BPPMaskPalette+0x3261c (bf9c219c)] ds:0023:bf9c219c=00000000 ===

win32k!EngMulDiv+0x2b68:
bf828828 0f8721fcffff    ja      win32k!EngMulDiv+0x278f (bf82844f)      [br=1]

win32k!EngMulDiv+0x278f:
bf82844f ff1580109abf    call    dword ptr [win32k!HT_Get8BPPMaskPalette+0x11500 (bf9a1080)] ds:0023:bf9a1080={nt!ExRaiseAccessViolation (809849aa)}

Comparing it with build 5000 (vbl_core.040809-2000)'s win32k.sys, the content of win32k!HT_Get8BPPMaskPalette+0x3261c (bf9c219c) in this build's win32k.sys is 7fff0000 instead of 00000000. At this point, the location of the failure has been pinpointed. With some additional comparison against build 5000 (vbl_core.040808-2000)'s win32k.sys, where that address is being filled up has been found:

This build's win32k.sys
Build 5000 (vbl_core.040809-2000) win32k.sys

Workarounds[edit | edit source]

Replace win32k.sys with build 5000 (vbl_core.040809-2000)'s, as comparing it against this build's win32k.sys turns up this only change and it will operate just as it was patched.

By using WinDbg: once breaking into the session, type:

ba e1 bf9c73b3 "r eax=7fff0000;e bf9c219c 00 00 ff 7f;gc"

It will now adjust the content of that address and continue.

Bugs and quirks[edit | edit source]

Windows Explorer[edit | edit source]

The details pane in Windows Explorer is broken, while the panes and tasks that do work cannot be opened or closed. In Control Panel, they also quickly disappear after loading. As such, the Classic view in Control Panel is almost impossible to access unless the user refreshes the page and quickly clicks on the option. This issue can be resolved by disabling the "Fade or slide menus into view" option in the Performance Options.