User Account Protection was the preliminary name for a core security component of Windows Vista. The component has now been officially named User Account Control (UAC).
![[Screenshot of default 'User Account Control Settings' from Windows 7]](https://technet.microsoft.com/en-us/library/images/ee424306.70a58d02-8dba-407a-9b75-f3ca55d54ad6.jpg "Screenshot of default 'User Account Control Settings' from Windows 7")
Windows Vista® introduced the
security featureUser Account Control: programs which want to be run with
administrativerights need to ask the user for consent.
This made some (really: a minority of) users quite angry: although
these (rather braindead) users continued to abuse
the administrative user account created during Windows
setup for their daily work (instead to follow best practice
and use a limited or standard user account), they had to answer a
prompt whenever they wanted to perform an administrative task.
Unfortunately Microsoft heard these users and weakened
the security feature
: Windows 7 introduced
auto elevation
and enabled it for some 70 programs shipped
with Windows 7 and later versions, which don’t
prompt for consent any more.
Due to flaws in the design and deficiencies in the implementation of
User Account Control, this security feature
(really: security theatre) can be bypassed
trivially in numerous ways when auto elevation
is enabled. As
result, arbitrary programs can then be run with
administrative
rights without prompting the user for
consent.
To defeat these trivial bypasses, auto elevation
must be
disabled by moving the slider of the
User Account Control setting to its highest position
titled Always notify
, as documented and shown in the
MSKB
articles
975787
and
4462938.
The slider position shown by the graphical user interface but does
not always match the effective setting: it shows
Always notify
even if the default setting
Notify me only when programs try to make changes to my computer
is configured!
![[Screenshot of 'Group Policy Object Editor' from Windows 7]](https://msdnshared.blob.core.windows.net/media/TNBlogsFS/BlogFileStorage/blogs_msdn/jamesfi/WindowsLiveWriter/ThebestwaytomakeUACshutupforawhile_11F33/image.png "[Screenshot of 'Group Policy Object Editor' from Windows 7]")
On default installations of Windows 7 or newer
versions of Windows NT perform the following 9 simple
steps.
Log on to the user account created during Windows setup.
Start one of the programs which have auto elevation
enabled,
MMC.exe or
WUSA.exe
for example: they start without prompting for consent.
Open Control Panel, then User Accounts and
click Change User Account Control setting
, then move the
slider to its highest position titled Always notify
and click
the button to apply the changed
setting.
Run the command line
"%SystemRoot%\System32\MMC.exe" "%SystemRoot%\System32\GPEdit.msc"
to start the Local Group Policy Editor snap-in of the
Microsoft Management Console, or run
the command line
"%SystemRoot%\System32\MMC.exe" "%SystemRoot%\System32\SecPol.msc"
to start the Local Security Policies snap-in, answer
the prompt for consent, then open the Local Policies
folder
and the Security Options
subfolder below: the policy
User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode
is shown as Prompt for consent on the secure desktop
,
properly matching the setting changed in step 3.
Repeat step 2.: both programs prompt for consent now.
Start RegEdit.exe, answer the
prompt for consent, then open the registry key
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
and delete the DWORD registry entry
ConsentPromptBehaviorAdmin present there.
Repeat step 4.: the policy
User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode
is now properly shown as Not Defined
.
Open Control Panel, then User Accounts
and click Change User Account Control setting
: the slider
is still shown in its highest position.
Repeat step 2.: both programs don’t
prompt for consent any more, despite the unchanged
slider position Always notify
!
setting, but abuses a registry entry reserved for a
policyinstead, it misinterprets the default policy value "Not Defined" and violates the now 25 year old Designed for Windows guidelines!
[HKEY_CURRENT_USER\Software\‹company name›\‹program name›]
"‹setting›"=…[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\‹program name›]
"‹setting›"=…[HKEY_CURRENT_USER\Software\Policies\‹company name›\‹program name›]
"‹policy›"=…[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\‹program name›]
"‹policy›"=…[HKEY_LOCAL_MACHINE\SOFTWARE\‹company name›\‹program name›]
"‹setting›"=…[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\‹program name›]
"‹setting›"=…[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\‹company name›\‹program name›]
"‹policy›"=…[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\‹program name›]
"‹policy›"=…Every process has an environment block that contains a set of environment variables and their values. There are two types of environment variables: user environment variables (set for each user) and system environment variables (set for everyone).By default, a child process inherits the environment variables of its parent process. […]
[…] To programmatically add or modify system environment variables, add them to the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment registry key, […]
Environment variables specify search paths for files, directories for temporary files, application-specific options, and other similar information. The system maintains an environment block for each user and one for the computer. The system environment block represents environment variables for all users of the particular computer. A user's environment block represents the environment variables the system maintains for that particular user, including the set of system environment variables.Both articles but fail to tell that two kinds of user environment variables exist, permanent and volatile, where they are stored, and how to add or modify them: permanent user environment variables are stored in the registry keyBy default, each process receives a copy of the environment block for its parent process. Typically, this is the environment block for the user who is logged on. […]
HKEY_CURRENT_USER\Environment alias
HKEY_USERS\‹security identifier›\Environment,
while volatile user environment variables are stored in the
(volatile) registry key
HKEY_CURRENT_USER\Volatile Environment alias
HKEY_USERS\‹security identifier›\Volatile Environment,
where they are created during user logon and discarded when the user
logs off.
The articles also fail to tell that not all system environment
variables are stored in the registry key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment:
the system environment variables ALLUSERSPROFILE,
COMPUTERNAME, PUBLIC,
CommonProgramFiles,
CommonProgramFiles(x86),
CommonProgramW6432,
ProgramData, ProgramFiles,
ProgramFiles(x86), ProgramW6432,
SystemDrive and SystemRoot are created
programmatically.
And they fail to tell that system environment variables are obscured by user environment variables of the same name – with but two notable exceptions:
Path are assigned to the process᾿
environment variable Path during user logon;
NT AUTHORITY\SYSTEM alias LocalSystem get
the system environment variables TEMP and
TMP instead of the respective user environment
variables!
Thanks
to the braindead (mis)behaviour
listed last, privileged processes running under the user account
NT AUTHORITY\SYSTEM alias LocalSystem use
the unsafe user-writable directory
%SystemRoot%\Temp\ instead of their private and
safe directory
%SystemRoot%\System32\Config\SystemProfile\AppData\Local\Temp\,
allowing unprivileged users to tamper with (executable) files
created there by these privileged processes, eventually resulting in
local escalation of privilege.
Note: see the Security Advisory ADV170017 for just one example of such a vulnerability.
%SystemRoot%\Profiles\%USERNAME%\
into new directories
%SystemDrive%\Documents and Settings\%USERNAME%\.
NT AUTHORITY\SYSTEM alias
LocalSystem
in the new directory
%SystemRoot%\System32\Config\SystemProfile\.
Note: its location was a rather braindead
choice, as it is subject to
file system direction
on 64-bit editions of Windows NT, where two separate
directories
%SystemRoot%\System32\Config\SystemProfile\ and
%SystemRoot%\SysWoW64\Config\SystemProfile\ exist!
The world-writable Temp
directory
%SystemRoot%\Temp\, shared by all users in previous
versions of Windows NT, was replaced with separate
private Temp
directories
%USERPROFILE%\Local Settings\Temp\ alias
%SystemDrive%\Documents and Settings\%USERNAME%\Local Settings\Temp\
located within the user profiles – except for
the LocalSystem user account, which continued (and
still continues) to use the (still world-writable) directory
%SystemRoot%\Temp\!
Windows XP added the (unprivileged) user accounts
NT AUTHORITY\LOCAL SERVICE alias
LocalService
and NT AUTHORITY\NETWORK SERVICE alias
NetworkService,
placed their user profiles in the directories
%SystemDrive%\Documents and Settings\LocalService\ and
%Systemdrive%\Documents and Settings\NetworkService\,
set their user environment variables TEMP and
TMP to %USERPROFILE%\Local Settings\Temp,
and created a private Temp
directory within both user
profiles.
Windows Vista relocated these two service profiles to
the new directories
%SystemRoot%\ServiceProfiles\LocalService\ and
%SystemRoot%\ServiceProfiles\NetworkService\, relocated
all normal user profiles
%SystemDrive%\Documents and Settings\%USERNAME%\ to
the directories %SystemDrive%\Users\%USERNAME%\, and
kept the profile
%SystemRoot%\System32\Config\SystemProfile\.
All user accounts except LocalSystem kept their private
Temp
directory, now
%USERPROFILE%\AppData\Local\Temp\ alias
%SystemDrive%\Users\%USERNAME%\AppData\Local\Temp\ for
the normal user accounts and
%SystemRoot%\ServiceProfiles\LocalService\AppData\Local\Temp\
respectively
%SystemRoot%\ServiceProfiles\NetworkService\AppData\Local\Temp\
for the service user accounts.
At least since Windows 7 the user environment variables
TEMP and TMP are set in the
LocalSystem user account too, despite
the directory %USERPROFILE%\AppData\Local\Temp\ alias
%SystemRoot%\System32\Config\SystemProfile\AppData\Local\Temp\
is missing in its user profile!
The MSDN article Profiles Directory provides additional information.
Create the text file quirk2.vbs with the following
content in an arbitrary directory:
' Copyright © 1999-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
Option Explicit
With WScript.CreateObject("WScript.Shell")
WScript.Echo "Environment Variables"
Dim strScope
For Each strScope In Array("PROCESS", "SYSTEM", "USER", "VOLATILE")
WScript.Echo
WScript.Echo "Scope '" & strScope & "': " & .Environment(strScope).Count & " items"
Dim strItem
For Each strItem In .Environment(strScope)
WScript.Echo vbTab & strItem
Next
Next
End With Execute the
VBScript
quirk2.vbs created in step 1. under the
LocalSystem user account to list the environment
variables of all scopes:
CScript.exe quirk2.vbs
Microsoft (R) Windows Script Host, Version 5.812 Copyright (C) Microsoft Corporation. All rights reserved. Environment Variables Scope 'PROCESS': 36 items =C:=C:\Windows\System32 =ExitCode=00000000 ALLUSERSPROFILE=C:\ProgramData APPDATA=C:\Windows\system32\config\systemprofile\AppData\Roaming CommonProgramFiles=C:\Program Files\Common Files CommonProgramFiles(x86)=C:\Program Files (x86)\Common Files CommonProgramW6432=C:\Program Files\Common Files COMPUTERNAME=AMNESIAC ComSpec=C:\Windows\system32\cmd.exe DriverData=C:\Windows\System32\Drivers\DriverData HOMEDRIVE=C: HOMEPATH=\Windows\system32 LOCALAPPDATA=C:\Windows\system32\config\systemprofile\AppData\Local NUMBER_OF_PROCESSORS=2 OS=Windows_NT Path=C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Windows\system32\config\systemprofile\AppData\Local\Microsoft\WindowsApps PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC PROCESSOR_ARCHITECTURE=AMD64 PROCESSOR_IDENTIFIER=Intel64 Family 6 Model 23 Stepping 10, GenuineIntel PROCESSOR_LEVEL=6 PROCESSOR_REVISION=170a ProgramData=C:\ProgramData ProgramFiles=C:\Program Files ProgramFiles(x86)=C:\Program Files (x86) ProgramW6432=C:\Program Files PROMPT=$P$G PSModulePath=%ProgramFiles%\WindowsPowerShell\Modules;C:\Windows\system32\WindowsPowerShell\v1.0\Modules PUBLIC=C:\Users\Public SystemDrive=C: SystemRoot=C:\Windows TEMP=C:\Windows\TEMP TMP=C:\Windows\TEMP USERDOMAIN=KANTHAK USERNAME=System USERPROFILE=C:\Windows\system32\config\systemprofile windir=C:\Windows Scope 'SYSTEM': 15 items ComSpec=%SystemRoot%\system32\cmd.exe DriverData=C:\Windows\System32\Drivers\DriverData OS=Windows_NT Path=%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\;%SYSTEMROOT%\System32\OpenSSH\ PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC PSModulePath=%SystemRoot%\system32\WindowsPowerShell\v1.0\Modules\ TEMP=%SystemRoot%\TEMP TMP=%SystemRoot%\TEMP USERNAME=SYSTEM windir=%SystemRoot% NUMBER_OF_PROCESSORS=2 PROCESSOR_ARCHITECTURE=AMD64 PROCESSOR_IDENTIFIER=Intel64 Family 6 Model 23 Stepping 10, GenuineIntel PROCESSOR_LEVEL=6 PROCESSOR_REVISION=170a Scope 'USER': 3 items PATH=%USERPROFILE%\AppData\Local\Microsoft\WindowsApps; TEMP=%USERPROFILE%\AppData\Local\Temp TMP=%USERPROFILE%\AppData\Local\Temp Scope 'VOLATILE': 0 items
Start the Command Processor under the
LocalSystem user account, then list (the contents of)
the directory %USERPROFILE%\AppData\Local\Temp\ alias
%SystemRoot%\System32\Config\SystemProfile\AppData\Local\Temp\
and all environment variables:
DIR "%USERPROFILE%\AppData\Local\Temp" /B SET
File Not Found ALLUSERSPROFILE=C:\ProgramData APPDATA=C:\Windows\system32\config\systemprofile\AppData\Roaming CommonProgramFiles=C:\Program Files\Common Files CommonProgramFiles(x86)=C:\Program Files (x86)\Common Files CommonProgramW6432=C:\Program Files\Common Files COMPUTERNAME=AMNESIAC ComSpec=C:\Windows\system32\cmd.exe DriverData=C:\Windows\System32\Drivers\DriverData HOMEDRIVE=C: HOMEPATH=\Windows\system32 LOCALAPPDATA=C:\Windows\system32\config\systemprofile\AppData\Local NUMBER_OF_PROCESSORS=2 OS=Windows_NT Path=C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Windows\system32\config\systemprofile\AppData\Local\Microsoft\WindowsApps PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC PROCESSOR_ARCHITECTURE=AMD64 PROCESSOR_IDENTIFIER=Intel64 Family 6 Model 23 Stepping 10, GenuineIntel PROCESSOR_LEVEL=6 PROCESSOR_REVISION=170a ProgramData=C:\ProgramData ProgramFiles=C:\Program Files ProgramFiles(x86)=C:\Program Files (x86) ProgramW6432=C:\Program Files PROMPT=$P$G PSModulePath=C:\Program Files\WindowsPowerShell\Modules;C:\Windows\system32\WindowsPowerShell\v1.0\Modules PUBLIC=C:\Users\Public SystemDrive=C: SystemRoot=C:\Windows TEMP=C:\Windows\TEMP TMP=C:\Windows\TEMP USERDOMAIN=KANTHAK USERNAME=System USERPROFILE=C:\Windows\system32\config\systemprofile windir=C:\Windows
Query the registry keys
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment,
HKEY_USERS\S-1-5-18\Environment and
HKEY_USERS\S-1-5-18\Volatile Environment to list the
environment variables stored in the registry:
Reg.exe QUERY "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" Reg.exe QUERY "HKEY_USERS\S-1-5-18\Environment" Reg.exe QUERY "HKEY_USERS\S-1-5-18\Volatile Environment"Note: the MSKB article 243300 gives the SID
S-1-5-18 for the NT AUTHORITY\SYSTEM
alias LocalSystem user account.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
ComSpec REG_EXPAND_SZ %SystemRoot%\system32\cmd.exe
DriverData REG_SZ C:\Windows\System32\Drivers\DriverData
NUMBER_OF_PROCESSORS REG_SZ 2
OS REG_SZ Windows_NT
Path REG_EXPAND_SZ %SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\;%SYSTEMROOT%\System32\OpenSSH\
PATHEXT REG_SZ .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
PROCESSOR_ARCHITECTURE REG_SZ AMD64
PROCESSOR_IDENTIFIER REG_SZ Intel64 Family 6 Model 23 Stepping 10, GenuineIntel
PROCESSOR_LEVEL REG_SZ 6
PROCESSOR_REVISION REG_SZ 170a
PSModulePath REG_EXPAND_SZ %ProgramFiles%\WindowsPowerShell\Modules;%SystemRoot%\system32\WindowsPowerShell\v1.0\Modules
TEMP REG_EXPAND_SZ %SystemRoot%\TEMP
TMP REG_EXPAND_SZ %SystemRoot%\TEMP
USERNAME REG_SZ SYSTEM
windir REG_EXPAND_SZ %SystemRoot%
HKEY_USERS\S-1-5-18\Environment
Path REG_EXPAND_SZ %USERPROFILE%\AppData\Local\Microsoft\WindowsApps;
TEMP REG_EXPAND_SZ %USERPROFILE%\AppData\Local\Temp
TMP REG_EXPAND_SZ %USERPROFILE%\AppData\Local\Temp
ERROR: The specified registry key or value was not found.
For comparision query the registry keys
HKEY_CURRENT_USER\Environment and
HKEY_CURRENT_USER\Volatile Environment of a standard
user account:
Reg.exe QUERY "HKEY_CURRENT_USER\Environment" Reg.exe QUERY "HKEY_CURRENT_USER\Volatile Environment" /S
HKEY_CURRENT_USER\Environment
Path REG_EXPAND_SZ %USERPROFILE%\AppData\Local\Microsoft\WindowsApps;
TEMP REG_EXPAND_SZ %USERPROFILE%\AppData\Local\Temp
TMP REG_EXPAND_SZ %USERPROFILE%\AppData\Local\Temp
HKEY_CURRENT_USER\Volatile Environment
LOGONSERVER REG_SZ \\AMNESIAC
USERDOMAIN REG_SZ AMNESIAC
USERNAME REG_SZ Stefan
USERPROFILE REG_SZ C:\Users\Stefan
HOMEPATH REG_SZ \Users\Stefan
HOMEDRIVE REG_SZ C:
APPDATA REG_SZ C:\Users\Stefan\AppData\Roaming
LOCALAPPDATA REG_SZ C:\Users\Stefan\AppData\Local
USERDOMAIN_ROAMINGPROFILE REG_SZ AMNESIAC
HKEY_CURRENT_USER\Volatile Environment\1
SESSIONNAME REG_SZ Console
CLIENTNAME REG_SZ
%SystemRoot%\System32\Config\SystemProfile\AppData\Local\Temp\,
then start the program
SystemPropertiesAdvanced.exe,
click the button ,
replace the value %SystemRoot%\TEMP of the system
environment variables TEMP and TMP with
%USERPROFILE%\AppData\Local\Temp, save the changed
setting and restart the system.
Note: a proper implementation calls functions like
GetSystemDirectory(),
GetSystemWow64Directory(),
GetWindowsDirectory(),
SHGetFolderPath()
and
SHGetKnownFolderPath()
to determine (system) paths instead to evaluate (user-controlled)
environment variables!
Write.exe,
RegEdit.exe,
NotePad.exe,
Explorer.exe as well as
IExplore.exe and
WordPad.exe
afterwards:
REM Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
CHDIR /D "%SystemRoot%"
FOR /F "Delims==" %? IN ('SET') DO @SET %?=
DIR Explorer.exe NotePad.exe RegEdit.exe Write.exe Win.ini /B
Write.exe
RegEdit.exe /M
NotePad.exe /P Win.ini
Explorer.exe /E,/Separate,.
START IExplore.exe
START WordPad.exe
EXIT
![[Screenshot of error message from 'WordPad' on Windows 7]](download/QUIRK3.PNG "[Screenshot of error message from 'WordPad' on Windows 7]")
explorer.exe notepad.exe regedit.exe write.exe win.ini…
For
command of the Command Processor
states:
The documentation for the builtin
- Parsing output
You can use the for /f command to parse the output of a command by making a back-quoted string from the Set between the parentheses. It is treated as a command line, which is passed to a child Cmd.exe. The output is captured into memory and parsed as if it is a file.
Start
command of the Command Processor
states:
- When you run a command that contains the string "CMD" as the first token without an extension or path qualifier, "CMD" is replaced with the value of the COMSPEC variable. This prevents users from picking up cmd from the current directory.
REM Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
CHDIR /D "%USERPROFILE%"
PUSHD "%SystemRoot%"
FOR /F "Delims==" %? IN ('SET') DO @SET %?=
START /B CMD /C SET
SET COMSPEC=%CD%\System32\Reg.exe
POPD
COPY NUL: Cmd.exe
FOR /F "Delims=" %? IN ('PAUSE') DO ECHO %?
FOR /F "Delims= UseBackQ" %? IN (`PAUSE`) DO ECHO %?
START CMD /C PAUSE
START /B ECHO
ASSOC | BREAK
FTYPE | SHIFT
SET | Cmd.exe
ERASE Cmd.exe
EXIT
COMSPEC=C:\Windows\System32\cmd.exe
PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.JS;.WS;.MSC
PROMPT=$P$G
1 File(s) copied.
Press any key . . .
Access Denied
Access Denied
ERROR: Invalid Argument/Option - '/c'.
Type "REG /?" for usage.
ERROR: Invalid Argument/Option - '/K'.
Type "REG /?" for usage.
ERROR: Invalid Argument/Option - '/S'.
Type "REG /?" for usage.
ERROR: Invalid Argument/Option - '/S'.
Type "REG /?" for usage.
ERROR: Invalid Argument/Option - '/S'.
Type "REG /?" for usage.
ERROR: Invalid Argument/Option - '/S'.
Type "REG /?" for usage.
ERROR: Invalid Argument/Option - '/S'.
Type "REG /?" for usage.
Access Denied
OUCH¹: contrary to its documentation,
FOR /F … IN ('…') DO … as well as
FOR /F "UseBackQ" … IN (`…`) DO …
executes the application determined by the value of the environment
variable COMSPEC (else the current process’
image) instead of Cmd.exe as child process.
OUCH²: contrary to its documentation,
START CMD … does not evaluate the environment
variable COMSPEC, but executes Cmd.exe
from the CWD
(else the current process᾿ image)!
OUCH³: when run in a pipeline, builtin
commands are executed in a child process determined by the value of
the environment variable COMSPEC.
The Command Processor sets the environment variables
COMSPEC, PATHEXT and PROMPT
if these are not provided by its caller.
COMSPEC is
a well-known weakness, documented as
CWE-73: External Control of File Name or Path
in the
CWE™,
allowing well-known attacks like
CAPEC-13: Subverting Environment Variable Values
documented in the
CAPEC™.
The (unintended) execution of (a rogue) Cmd.exe from
the CWD
constitutes a security vulnerability, similar to
CVE-2014-0315
alias
MS14-019
I discovered about 6 years ago, which was fixed with security update
2922229
back then.
Note: the post MS14-019 – Fixing a binary hijacking via .cmd or .bat file on Microsoft’s Security Research and Defense Blog provides additional information.
The well-known underlying weakness is documented as CWE-426: Untrusted Search Path and CWE-427: Uncontrolled Search Path Element, the well-known attack is documented as CAPEC-471: Search Order Hijacking.
They replied with the following statements:
The engineering team has looked over the issue and has stated that this appears to be a documentation error and has been handed over to the team owning that site. In this case this does not appear to be a vulnerability and we will be closing it out on our side. The method of using this information in an attack would require a remote attacker to find malicious program that uses theOUCH: it appears to me that the engineering team is wrong!START cmdand trick the user to trigger this program as a minimum.
Call
command of the Command Processor
states:
Calls one batch program from another without stopping the parent batch program. The call command accepts labels as the target of the call.Note
Call has no effect at the command prompt when it is used outside of a script or batch file.
REM Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de> CALL Reg(Dummy CALL Reg,Dummy CALL Reg;Dummy CALL Reg=Dummy FOR %? IN (First,Second;Third=Fourth) DO @ECHO %? EXIT
ERROR: Invalid Argument/Option - '(Dummy'. Type "REG /?" for usage. ERROR: Invalid Argument/Option - ',Dummy'. Type "REG /?" for usage. ERROR: Invalid Argument/Option - ';Dummy'. Type "REG /?" for usage. ERROR: Invalid Argument/Option - '=Dummy'. Type "REG /?" for usage. First Second Third FourthOUCH¹: the Command Processor mistreats valid filenames containing an opening parenthesis '
(', a comma ',', a
semicolon ';' or an equals sign '=', and
interprets these characters as separator!
OUCH²: contrary to its documentation,
CALL does not just call batch scripts and has effect at
the command prompt.
OUCH³: in builtin commands, the
Command Processor mistreats comma, semicolon and equals
sign almost always as delimiter or separator, and sometimes like
white space
.
GetFileMUIInfo()
is documented in the
MSDN as
follows:
The description of its behaviour is but wrong and misleading![…]BOOL GetFileMUIInfo( DWORD dwFlags, PCWSTR pcwszFilePath, PFILEMUIINFO pFileMUIInfo, DWORD *pcbFileMUIInfo );
pFileMUIInfo
[…]
Alternatively, the application can set this parameter to NULL if pcbFileMUIInfo is set to 0. In this case, the function retrieves the required size for the information buffer in pcbFileMUIInfo.
[…]
pcbFileMUIInfo
[…]
Alternatively, the application can set this parameter to 0 if it sets NULL in pFileMUIInfo. In this case, the function retrieves the required file information buffer size in pcbFileMUIInfo. To allocate the correct amount of memory, this value should be added to the size of theFILEMUIINFOstructure itself.
The initial call of
GetFileMUIInfo()
for any module, with address and size of the buffer given as
NULL and 0, fails (expected) with error 122 alias
ERROR_INSUFFICIENT_BUFFER,
but always returns 84 as (additional) buffer size;
subsequent calls then return the full buffer size.
The returned (additional or full) buffer size is but not always
sufficient; subsequent calls can fail again with error 122 alias
ERROR_INSUFFICIENT_BUFFER, so additional calls with the
buffer size returned from the previous call are then necessary until
the call finally succeeds!
Note: implemented properly, the first call would return the correct (full) buffer size and grant a successful second call, as documented (for example) in the MSDN article Retrieving Data of Unknown Length!
Create the text file quirk6.c with the following
content in an arbitrary, preferable empty directory:
// Copyright © 2009-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
#pragma comment(compiler)
#pragma comment(linker, "/DEFAULTLIB:KERNEL32.LIB")
#pragma comment(linker, "/DEFAULTLIB:USER32.LIB")
#pragma comment(linker, "/ENTRY:wmainCRTStartup")
#pragma comment(linker, "/SUBSYSTEM:CONSOLE")
#pragma comment(user, __TIMESTAMP__)
#define STRICT
#define UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
__declspec(safebuffers)
BOOL PrintConsole(HANDLE hConsole, LPCWSTR lpFormat, ...)
{
WCHAR szBuffer[1025];
DWORD dwBuffer;
DWORD dwConsole;
va_list vaInserts;
va_start(vaInserts, lpFormat);
dwBuffer = wvsprintf(szBuffer, lpFormat, vaInserts);
va_end(vaInserts);
if (dwBuffer == 0)
return FALSE;
if (!WriteConsole(hConsole, szBuffer, dwBuffer, &dwConsole, NULL))
return FALSE;
return dwConsole == dwBuffer;
}
const WCHAR szModule[] = L"C:\\Windows\\RegEdit.exe";
__declspec(noreturn)
VOID WINAPI wmainCRTStartup(VOID)
{
PFILEMUIINFO lpFileMUIInfo = NULL;
DWORD dwFileMUIInfo = 0;
DWORD dwError = ERROR_SUCCESS;
HANDLE hConsole = GetStdHandle(STD_ERROR_HANDLE);
if (GetFileMUIInfo(MUI_QUERY_CHECKSUM | MUI_QUERY_LANGUAGE_NAME | MUI_QUERY_RESOURCE_TYPES | MUI_QUERY_TYPE,
szModule, lpFileMUIInfo, &dwFileMUIInfo))
PrintConsole(hConsole,
L"GetFileMUIInfo() returned success %lu and buffer size %lu for module \'%ls\'\n",
dwError = GetLastError(), dwFileMUIInfo, szModule);
else
{
PrintConsole(hConsole,
L"GetFileMUIInfo() returned error %lu and buffer size %lu for module \'%ls\'\n",
dwError = GetLastError(), dwFileMUIInfo, szModule);
dwFileMUIInfo += sizeof(FILEMUIINFO);
while (dwError == ERROR_INSUFFICIENT_BUFFER)
{
lpFileMUIInfo = LocalAlloc(LPTR, dwFileMUIInfo);
if (lpFileMUIInfo == NULL)
PrintConsole(hConsole,
L"LocalAlloc() returned error %lu\n",
dwError = GetLastError());
else
{
lpFileMUIInfo->dwSize = dwFileMUIInfo;
lpFileMUIInfo->dwVersion = MUI_FILEINFO_VERSION;
if (GetFileMUIInfo(MUI_QUERY_CHECKSUM | MUI_QUERY_LANGUAGE_NAME | MUI_QUERY_RESOURCE_TYPES | MUI_QUERY_TYPE,
szModule, lpFileMUIInfo, &dwFileMUIInfo))
PrintConsole(hConsole,
L"GetFileMUIInfo() returned success %lu and buffer size %lu for module \'%ls\'\n",
dwError = GetLastError(), dwFileMUIInfo, szModule);
else
PrintConsole(hConsole,
L"GetFileMUIInfo() returned error %lu and buffer size %lu for module \'%ls\'\n",
dwError = GetLastError(), dwFileMUIInfo, szModule);
if (LocalFree(lpFileMUIInfo) != NULL)
PrintConsole(hConsole,
L"LocalFree() returned error %lu\n",
GetLastError());
}
}
}
ExitProcess(dwError);
} Build the application quirk6.exe from the source file
quirk6.c created in step 1.:
CL.EXE /GA /GF /Tcquirk6.c /W4 /ZlNote: if necessary, see the MSDN article
Use the Microsoft C++ toolset from the command linefor an introduction.
Note: quirk6.exe is a pure
Win32 application and builds without the
MSVCRT
libraries.
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. quirk6.c Microsoft (R) Incremental Linker Version 10.00.40219.386 Copyright (C) Microsoft Corporation. All rights reserved. /out:quirk6.exe quirk6.obj
Execute the application quirk6.exe built in
step 2. to demonstrate the (mis)behaviour of the
Win32 function
GetFileMUIInfo():
.\quirk6.exe
GetFileMUIInfo() returned error 122 and buffer size 84 for module 'C:\Windows\RegEdit.exe' GetFileMUIInfo() returned error 122 and buffer size 166 for module 'C:\Windows\RegEdit.exe' GetFileMUIInfo() returned error 122 and buffer size 180 for module 'C:\Windows\RegEdit.exe' GetFileMUIInfo() returned success 0 and buffer size 180 for module 'C:\Windows\RegEdit.exe'
GetTempPath()
and
GetTempFileName()
are documented in the
MSDN as
follows:
In addition to the[…]DWORD GetTempPath( DWORD nBufferLength, LPTSTR lpBuffer );The maximum possible return value is MAX_PATH+1 (261).
[…]
The GetTempPath function checks for the existence of environment variables in the following order and uses the first path found:
- The path specified by the TMP environment variable.
- The path specified by the TEMP environment variable.
- The path specified by the USERPROFILE environment variable.
- The Windows directory.
lpBuffer
can be 0 alias NULL if nBufferLength is 0.
[…]UINT GetTempFileName( LPCTSTR lpPathName, LPCTSTR lpPrefixString, UINT uUnique, LPTSTR lpTempFileName );
lpPathNameThe directory path for the file name. Applications typically specify a period (.) for the current directory or the result of the GetTempPath function. The string cannot be longer than MAX_PATH−14 characters or GetTempFileName will fail.
Create the text file quirk7.c with the following
content in an arbitrary, preferable empty directory:
// Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
#pragma comment(compiler)
#pragma comment(linker, "/DEFAULTLIB:KERNEL32.LIB")
#pragma comment(linker, "/DEFAULTLIB:USER32.LIB")
#pragma comment(linker, "/ENTRY:wmainCRTStartup")
#pragma comment(linker, "/SUBSYSTEM:CONSOLE")
#pragma comment(user, __TIMESTAMP__)
#define STRICT
#define UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
__declspec(safebuffers)
BOOL PrintConsole(HANDLE hConsole, LPCWSTR lpFormat, ...)
{
WCHAR szBuffer[1025];
DWORD dwBuffer;
DWORD dwConsole;
va_list vaInserts;
va_start(vaInserts, lpFormat);
dwBuffer = wvsprintf(szBuffer, lpFormat, vaInserts);
va_end(vaInserts);
if (dwBuffer == 0)
return FALSE;
if (!WriteConsole(hConsole, szBuffer, dwBuffer, &dwConsole, NULL))
return FALSE;
return dwConsole == dwBuffer;
}
__declspec(noreturn)
VOID wmainCRTStartup(VOID)
{
WCHAR szBuffer[MAX_PATH + 2];
DWORD dwBuffer;
DWORD dwError = ERROR_SUCCESS;
HANDLE hConsole = GetStdHandle(STD_ERROR_HANDLE);
if (hConsole == INVALID_HANDLE_VALUE)
dwError = GetLastError();
else
{
dwBuffer = GetTempPath(sizeof(szBuffer) / sizeof(*szBuffer), szBuffer);
if (dwBuffer == 0)
PrintConsole(hConsole,
L"GetTempPath() returned error %lu\n",
dwError = GetLastError());
else
{
PrintConsole(hConsole,
L"GetTempPath() returned pathname \'%ls\' of length %lu\n",
szBuffer, dwBuffer);
if (GetTempFileName(szBuffer, L"tmp", 0, szBuffer) == 0)
PrintConsole(hConsole,
L"GetTempFileName() returned error %lu\n",
dwError = GetLastError());
else
{
PrintConsole(hConsole,
L"GetTempFileName() returned pathname \'%ls\'\n",
szBuffer);
if (!DeleteFile(szBuffer))
PrintConsole(hConsole,
L"DeleteFile() returned error %lu\n",
dwError = GetLastError());
}
}
}
ExitProcess(dwError);
} Build the application quirk7.exe from the source file
quirk7.c created in step 1.:
CL.EXE /GA /GF /Tcquirk7.c /W4 /ZlNote: if necessary, see the MSDN article
Use the Microsoft C++ toolset from the command linefor an introduction.
Note: quirk7.exe is a pure
Win32 application and builds without the
MSVCRT
libraries.
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. quirk7.c Microsoft (R) Incremental Linker Version 10.00.40219.386 Copyright (C) Microsoft Corporation. All rights reserved. /out:quirk7.exe quirk7.obj
Create the text file quirk7.cmd with the following
content in the directory used in the previous steps 1. and 2.:
REM Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
SETLOCAL
CHDIR /D "%ALLUSERSPROFILE%"
SET T
@"%~dpn0.exe"
SET TMP=
@"%~dpn0.exe"
SET TEMP=
@"%~dpn0.exe"
SET USERPROFILE=
@"%~dpn0.exe"
SET USERPROFILE=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz
@"%~dpn0.exe"
SET USERPROFILE=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz
@"%~dpn0.exe"
SET TEMP=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy
@"%~dpn0.exe"
SET TMP=%SystemDrive%\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvw
@"%~dpn0.exe"
SET TMP=%SystemDrive%\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuv
@"%~dpn0.exe"
SET TMP=.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.
@"%~dpn0.exe"
SET TMP=.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.
@"%~dpn0.exe"
SET TMP=..
@"%~dpn0.exe"
EXIT /B Execute the batch script quirk7.cmd created in
step 3. on Windows 7 (or an earlier version):
.\quirk7.cmd
REM Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de> SETLOCAL CHDIR /D "C:\ProgramData" SET T TEMP=C:\Users\Stefan\AppData\Local\Temp TMP=C:\Users\Stefan\AppData\Local\Temp GetTempPath() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\' of length 35 GetTempFileName() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\tmp8D8B.tmp' SET TMP= GetTempPath() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\' of length 35 GetTempFileName() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\tmp8D9B.tmp' SET TEMP= GetTempPath() returned pathname 'C:\Users\Stefan\' of length 16 GetTempFileName() returned pathname 'C:\Users\Stefan\tmp8DAB.tmp' SET USERPROFILE= GetTempPath() returned pathname 'C:\Windows\' of length 11 GetTempFileName() returned pathname 'C:\Windows\tmp8E01.tmp' SET USERPROFILE=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz GetTempPath() returned pathname 'C:\Windows\' of length 11 GetTempFileName() returned pathname 'C:\Windows\tmp8E33.tmp' SET USERPROFILE=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz GetTempPath() returned pathname 'C:\Windows\' of length 11 GetTempFileName() returned pathname 'C:\Windows\tmp8E55.tmp' SET TEMP=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy GetTempPath() returned pathname 'C:\ProgramData\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy\' of length 145 GetTempFileName() returned error 267 SET TMP=C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvw GetTempPath() returned pathname 'C:\ProgramData\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy\' of length 145 GetTempFileName() returned error 267 SET TMP=C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuv GetTempPath() returned pathname 'C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuv\' of length 130 GetTempFileName() returned error 267 SET TMP=.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\. GetTempPath() returned pathname 'C:\ProgramData\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy\' of length 145 GetTempFileName() returned error 267 SET TMP=.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\. GetTempPath() returned pathname 'C:\ProgramData\' of length 15 GetTempFileName() returned pathname 'C:\ProgramData\tmp8EDD.tmp' SET TMP=.. GetTempPath() returned pathname 'C:\' of length 3 GetTempFileName() returned pathname 'C:\tmp8EFF.tmp' EXIT /BOUCH¹: the environment variables
TMP, TEMP and USERPROFILE are
discarded on Windows 7 and earlier versions if their
value is not less than 130
(= MAX_PATH ÷ 2) characters!
OUCH²: although the directory name is valid,
GetTempFileName()
fails with Win32 error 267 alias
ERROR_DIRECTORY,
i.e. The directory name is invalid.
instead of error 3 alias
ERROR_PATH_NOT_FOUND,
i.e. The system cannot find the path specified.
Execute the batch script quirk7.cmd created in
step 3. on Windows 8 (or a later version):
.\quirk7.cmd
REM Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de> SETLOCAL CHDIR /D "C:\ProgramData" SET T TEMP=C:\Users\Stefan\AppData\Local\Temp TMP=C:\Users\Stefan\AppData\Local\Temp GetTempPath() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\' of length 35 GetTempFileName() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\tmpF791.tmp' SET TMP= GetTempPath() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\' of length 35 GetTempFileName() returned pathname 'C:\Users\Stefan\AppData\Local\Temp\tmpF7A1.tmp' SET TEMP= GetTempPath() returned pathname 'C:\Users\Stefan\' of length 16 GetTempFileName() returned pathname 'C:\Users\Stefan\tmpF7A9.tmp' SET USERPROFILE= GetTempPath() returned pathname 'C:\Windows\' of length 11 GetTempFileName() returned pathname 'C:\Windows\tmpF7B1.tmp' SET USERPROFILE=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz GetTempPath() returned pathname '' of length 277 GetTempFileName() returned pathname '\tmpF7C7.tmp' SET USERPROFILE=abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz GetTempPath() returned pathname 'C:\ProgramData\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz\' of length 146 GetTempFileName() returned error 267 SET TEMP=C:\ProgramData\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy GetTempPath() returned pathname 'C:\ProgramData\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy\' of length 145 GetTempFileName() returned error 267 SET TMP=C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvw GetTempPath() returned pathname 'C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvw\' of length 131 GetTempFileName() returned error 267 SET TMP=C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuv GetTempPath() returned pathname 'C:\abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuv\' of length 130 GetTempFileName() returned error 267 SET TMP=.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\. GetTempPath() returned pathname '' of length 276 GetTempFileName() returned pathname '\tmpF7D1.tmp' SET TMP=.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\.\. GetTempPath() returned pathname 'C:\ProgramData\' of length 15 GetTempFileName() returned pathname 'C:\ProgramData\tmpF7D9.tmp' SET TMP=.. GetTempPath() returned pathname 'C:\' of length 3 GetTempFileName() returned pathname 'C:\tmpF7DF.tmp' EXIT /BOUCH³: contrary to its documentation cited above, the Win32 function
GetTempPath()
returns values greater than MAX_PATH + 1!
OUCH: the documentation also fails to tell that the
Win32 function
GetTempFileName()
adds a backslash in front of the filename if the directory path does
not end with a backslash!
GetEnvironmentVariable()
is documented in the
MSDN as
follows:
Note: designed and implemented properly, this function would return the value of[…]DWORD GetEnvironmentVariable( LPCTSTR lpName, LPTSTR lpBuffer, DWORD nSize );
nSizeThe size of the buffer pointed to by the lpBuffer parameter, including the null-terminating character, in characters. […]
If the function fails, the return value is zero. If the specified environment variable was not found in the environment block, GetLastError returns ERROR_ENVVAR_NOT_FOUND.
nSize for failure!
In addition to the quirk bug demonstrated
below, the documentation fails to tell that lpBuffer
can be 0 alias NULL if nSize is 0.
It also shows a VERY common mistake: there is no
null-terminating character
, but a
(string-)terminating
!
NUL character
Create the text file quirk8.c with the following
content in an arbitrary, preferable empty directory:
// Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
#pragma comment(compiler)
#pragma comment(linker, "/DEFAULTLIB:KERNEL32.LIB")
#pragma comment(linker, "/DEFAULTLIB:USER32.LIB")
#pragma comment(linker, "/ENTRY:wmainCRTStartup")
#pragma comment(linker, "/SUBSYSTEM:CONSOLE")
#pragma comment(user, __TIMESTAMP__)
#define STRICT
#define UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
__declspec(safebuffers)
BOOL PrintConsole(HANDLE hConsole, LPCWSTR lpFormat, ...)
{
WCHAR szBuffer[1025];
DWORD dwBuffer;
DWORD dwConsole;
va_list vaInserts;
va_start(vaInserts, lpFormat);
dwBuffer = wvsprintf(szBuffer, lpFormat, vaInserts);
va_end(vaInserts);
if (dwBuffer == 0)
return FALSE;
if (!WriteConsole(hConsole, szBuffer, dwBuffer, &dwConsole, NULL))
return FALSE;
return dwConsole == dwBuffer;
}
__declspec(noreturn)
VOID wmainCRTStartup(VOID)
{
WCHAR szBuffer[MAX_PATH];
DWORD dwBuffer;
DWORD dwCount;
DWORD dwError = ERROR_SUCCESS;
HANDLE hConsole = GetStdHandle(STD_ERROR_HANDLE);
if (hConsole == INVALID_HANDLE_VALUE)
dwError = GetLastError();
else
if (!SetEnvironmentVariable(L"EMPTY", L""))
PrintConsole(hConsole,
L"SetEnvironmentVariable(\"EMPTY\", \"\") returned error %lu\n",
dwError = GetLastError());
else
{
dwBuffer = GetEnvironmentVariable(L"EMPTY", szBuffer, 0);
if (dwBuffer == 0)
PrintConsole(hConsole,
L"GetEnvironmentVariable(\"EMPTY\", 0x%p, 0) returned error %lu\n",
szBuffer, dwError = GetLastError());
else
{
PrintConsole(hConsole,
L"GetEnvironmentVariable(\"EMPTY\", 0x%p, 0) returned buffer size %lu\n",
szBuffer, dwBuffer);
SetLastError('FAIL');
dwCount = GetEnvironmentVariable(L"EMPTY", szBuffer, dwBuffer);
if (dwCount == 0)
PrintConsole(hConsole,
L"GetEnvironmentVariable(\"EMPTY\", 0x%p, %lu) returned error %lu\n",
szBuffer, dwBuffer, dwError = GetLastError());
}
}
ExitProcess(dwError);
} Build the application quirk8.exe from the source file
quirk8.c created in step 1.:
CL.EXE /GA /GF /Tcquirk8.c /W4 /ZlNote: if necessary, see the MSDN article
Use the Microsoft C++ toolset from the command linefor an introduction.
Note: quirk8.exe is a pure
Win32 application and builds without the
MSVCRT
libraries.
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. quirk8.c Microsoft (R) Incremental Linker Version 10.00.40219.386 Copyright (C) Microsoft Corporation. All rights reserved. /out:quirk8.exe quirk8.obj
Execute the application quirk8.exe built in
step 2. to demonstrate the (mis)behaviour:
.\quirk8.exe
GetEnvironmentVariable("EMPTY", 0x0037F884, 0) returned buffer size 1
GetEnvironmentVariable("EMPTY", 0x0037F884, 1) returned error 1178683724
OUCH: for environment variables with empty value,
the Win32 function
GetEnvironmentVariable()
returns 0, but fails to (re)set the Win32 error 0 alias
ERROR_SUCCESS
to indicate no error!
GetDllDirectory()
is documented in the
MSDN as
follows:
Note: designed and implemented properly, this function would return the value of[…]DWORD GetDllDirectory( DWORD nBufferLength, LPTSTR lpBuffer );If the function succeeds, the return value is the length of the string copied to lpBuffer, in characters, not including the terminating null character. If the return value is greater than nBufferLength, it specifies the size of the buffer required for the path.
If the function fails, the return value is zero. To get extended error information, call GetLastError.
nBufferLength for
failure!
In addition to the quirk bug demonstrated
below, the documentation fails to tell that lpBuffer
can be 0 alias NULL if nBufferLength is 0.
Create the text file quirk9.c with the following
content in an arbitrary, preferable empty directory:
// Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
#pragma comment(compiler)
#pragma comment(linker, "/DEFAULTLIB:KERNEL32.LIB")
#pragma comment(linker, "/DEFAULTLIB:USER32.LIB")
#pragma comment(linker, "/ENTRY:wmainCRTStartup")
#pragma comment(linker, "/SUBSYSTEM:CONSOLE")
#pragma comment(user, __TIMESTAMP__)
#define STRICT
#define UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
__declspec(safebuffers)
BOOL PrintConsole(HANDLE hConsole, LPCWSTR lpFormat, ...)
{
WCHAR szBuffer[1025];
DWORD dwBuffer;
DWORD dwConsole;
va_list vaInserts;
va_start(vaInserts, lpFormat);
dwBuffer = wvsprintf(szBuffer, lpFormat, vaInserts);
va_end(vaInserts);
if (dwBuffer == 0)
return FALSE;
if (!WriteConsole(hConsole, szBuffer, dwBuffer, &dwConsole, NULL))
return FALSE;
return dwConsole == dwBuffer;
}
__declspec(noreturn)
VOID wmainCRTStartup(VOID)
{
WCHAR szBuffer[MAX_PATH];
DWORD dwBuffer;
DWORD dwCount;
DWORD dwError = ERROR_SUCCESS;
HANDLE hConsole = GetStdHandle(STD_ERROR_HANDLE);
if (hConsole == INVALID_HANDLE_VALUE)
dwError = GetLastError();
else
{
dwBuffer = GetDllDirectory(0, szBuffer);
if (dwBuffer == 0)
PrintConsole(hConsole,
L"GetDllDirectory(0, 0x%p) returned error %lu\n",
szBuffer, dwError = GetLastError());
else
{
PrintConsole(hConsole,
L"GetDllDirectory(0, 0x%p) returned buffer size %lu\n",
szBuffer, dwBuffer);
SetLastError('FAIL');
dwCount = GetDllDirectory(dwBuffer, szBuffer);
if (dwCount == 0)
PrintConsole(hConsole,
L"GetDllDirectory(%lu, 0x%p) returned error %lu\n",
dwBuffer, szBuffer, dwError = GetLastError());
}
}
ExitProcess(dwError);
} Build the application quirk9.exe from the source file
quirk9.c created in step 1.:
CL.EXE /GA /GF /Tcquirk9.c /W4 /ZlNote: if necessary, see the MSDN article
Use the Microsoft C++ toolset from the command linefor an introduction.
Note: quirk9.exe is a pure
Win32 application and builds without the
MSVCRT
libraries.
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. quirk9.c Microsoft (R) Incremental Linker Version 10.00.40219.386 Copyright (C) Microsoft Corporation. All rights reserved. /out:quirk9.exe quirk9.obj
Execute the application quirk9.exe built in
step 2. to demonstrate the (mis)behaviour:
.\quirk9.exe
GetDllDirectory(0, 0x003EF948) returned buffer size 1 GetDllDirectory(1, 0x003EF948) returned error 1178683724OUCH: when no application-specific DLL search path is set, the Win32 function
GetDllDirectory()
returns 0, but fails to (re)set the Win32 error 0 alias
ERROR_SUCCESS
to indicate no error!
DefWindowProc()
and
PostQuitMessage()
functions are documented in the
MSDN as
follows:
Calls the default window procedure to provide default processing for any window messages that an application does not process. This function ensures that every message is processed. DefWindowProc is called with the same parameters received by the window procedure.
Indicates to the system that a thread has made a request to terminate (quit). It is typically used in response to a WM_DESTROY message.The
WM_NCCREATE
message is documented in the
MSDN as
follows:
Sent prior to the WM_CREATE message when a window is first created.A window receives this message through its WindowProc function.
[…]
If an application processes this message, it should return TRUE to continue creation of the window. If the application returns FALSE, the CreateWindow or CreateWindowEx function will return a NULL handle.
Create the text file quirk10.c with the following
content in an arbitrary, preferable empty directory:
// Copyright © 2004-2020, Stefan Kanthak <stefan.kanthak@nexgo.de>
#pragma comment(compiler)
#pragma comment(linker, "/DEFAULTLIB:KERNEL32.LIB")
#pragma comment(linker, "/DEFAULTLIB:USER32.LIB")
#pragma comment(linker, "/ENTRY:wmainCRTStartup")
#pragma comment(linker, "/SUBSYSTEM:CONSOLE")
#pragma comment(user, __TIMESTAMP__)
#define STRICT
#define UNICODE
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
LRESULT WINAPI WindowProc(HWND hWindow,
UINT uMessage,
WPARAM wParam,
LPARAM lParam)
{
switch (uMessage)
{
#if QUIRKS == 1 // DefWindowProc() must be called in response to the
// WM_NCCREATE message to register the window title!
case WM_NCCREATE:
return (LRESULT) TRUE;
#endif
case WM_DESTROY:
PostQuitMessage(0);
// case WM_NULL:
// case WM_NCDESTROY:
// case WM_CREATE:
return (LRESULT) 0;
default:
return DefWindowProc(hWindow, uMessage, wParam, lParam);
}
}
extern const IMAGE_DOS_HEADER __ImageBase;
__declspec(noreturn)
VOID wmainCRTStartup(VOID)
{
DWORD dwError;
LRESULT lResult;
BOOL bResult;
HWND hWindow;
MSG msg;
WNDCLASSEX wce = {sizeof(WNDCLASSEX),
CS_GLOBALCLASS,
#if QUIRKS == 2 // DefWindowProc() does not call PostQuitMessage()
// in response to the WM_DESTROY message!
DefWindowProc,
#else
WindowProc,
#endif
0,
0,
(HINSTANCE) &__ImageBase,
(HICON) NULL,
(HCURSOR) NULL,
(HBRUSH) COLOR_BACKGROUND,
(LPCWSTR) NULL,
L"Quirks Demonstration Class",
(HICON) NULL};
ATOM atom = RegisterClassEx(&wce);
if (atom == 0)
dwError = GetLastError();
else
{
hWindow = CreateWindowEx(WS_EX_APPWINDOW,
wce.lpszClassName,
L"Quirks Demonstration Window",
WS_OVERLAPPEDWINDOW | WS_VISIBLE,
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
(HWND) NULL,
(HMENU) NULL,
wce.hInstance,
NULL);
if (hWindow == NULL)
dwError = GetLastError();
else
{
while ((bResult = GetMessage(&msg, (HWND) NULL, 0, 0)) > 0)
{
if (TranslateMessage(&msg))
;
lResult = DispatchMessage(&msg);
}
dwError = bResult < 0 ? GetLastError() : msg.wParam;
}
if (!UnregisterClass(wce.lpszClassName, wce.hInstance))
dwError = GetLastError();
}
ExitProcess(dwError);
} Build the application quirk10.exe from the source file
quirk10.c created in step 1. with the macro
QUIRKS defined as 2:
CL.EXE /DQUIRKS=2 /GA /GF /Tcquirk10.c /W4 /ZlNote: if necessary, see the MSDN article
Use the Microsoft C++ toolset from the command linefor an introduction.
Note: quirk10.exe is a pure
Win32 application and builds without the
MSVCRT
libraries.
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. quirk10.c Microsoft (R) Incremental Linker Version 10.00.40219.386 Copyright (C) Microsoft Corporation. All rights reserved. /out:quirk10.exe quirk10.obj
Start the application quirk10.exe built in step 2.
and close its window to demonstrate the first (mis)behaviour:
.\quirk10.exeOUCH¹: although the application window titled
Quirks Demonstration Windowwas closed, the Command Processor waits for the child process to terminate … until you press Ctrl C!
Contrary to its documentation cited above, the Win32
function
DefWindowProc()
fails to provide the typical response to the
WM_DESTROY
message, i.e. it does not call
PostQuitMessage(),
so the process’ primary thread does not
terminate!
Build the application quirk10.exe from the source file
quirk10.c created in step 1. again, now with the
macro QUIRKS defined as 1:
CL.EXE /DQUIRKS=1 /GA /GF /Tcquirk10.c /W4 /Zl
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. quirk10.c Microsoft (R) Incremental Linker Version 10.00.40219.386 Copyright (C) Microsoft Corporation. All rights reserved. /out:quirk10.exe quirk10.obj
Start the application quirk10.exe built in step 4.
to demonstrate the second (mis)behaviour:
.\quirk10.exe
![[Screenshot of untitled application window on Windows XP]](download/Quirk10_Classic.png "[Screenshot of untitled application window on Windows XP]")
![[Screenshot of untitled application window on Windows 7]](download/Quirk10_Aero.png "[Screenshot of untitled application window on Windows 7]")
![[Screenshot of untitled application window on Windows 10]](download/Quirk10_Metro.png "[Screenshot of untitled application window on Windows 10]")
Quirks Demonstration Window!
Contrary to the documentation cited above, an application’s
WindowProc()
must not return TRUE in response to
the
WM_NCCREATE
message, but needs to call the
DefWindowProc()
function instead!
Gates particlewith a mass equivalent to some 100 G$.
Use the X.509 certificate to send S/MIME encrypted mail.
Note: email in weird format and without a proper sender name is likely to be discarded!
I dislike
HTML (and even
weirder formats too) in email, I prefer to receive plain text.
I also expect to see your full (real) name as sender, not your
nickname.
I abhor top posts and expect inline quotes in replies.
as iswithout any warranty, neither express nor implied.
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