Jet Expression Can Execute Unsafe Visual Basic for Applications Functions

ID: Q239104

The information in this article applies to:

Microsoft ODBC Driver for Access, version 3.5
Microsoft Access versions 7.0, 97
Microsoft Office Pro 97

Moderate: Requires basic macro, coding, and interoperability skills.

SYMPTOMS

Using Jet 3.5x, a user can call unsafe Visual Basic for Applications functions in query statements from all types of Jet applications, such as ODBC or Access. For example, the following statement would result in all files being deleted from a computer's current folder:

SELECT Shell("Cmd /c del *.*") As c1 From Customers

NOTE: The Shell command in this example works in Microsoft Windows NT. The command would have to be modified as follows to work on a computer running Microsoft Windows 95/98:

SELECT Shell("Command.com /c del *.*") As c1 From Customers

The security risk occurs when expressions contain Visual Basic for Application commands that can be harmful to a computer running the query, for example, Shell commands to delete files or format the computer.

CAUSE

Jet queries can contain Visual Basic for Applications expressions. These are evaluated during query execution, a behavior that is desirable in many circumstances. However, if part of the query contains the Shell command, it is parsed and executed on the computer.

You can block such operations, which is called "Sandbox mode." However, by default in Microsoft Jet 3.5x, Sandbox mode is not enabled for any applications that can issue Visual Basic for Applications commands.

RESOLUTION

In order to enable Sandbox mode, you must first install the Microsoft Jet 3.5 SP3 update. After installing this update, the next time that you run Jet, a new registry key is added to the registry. You can use this new registry key to prevent this type of security risk. The following is the registry key that is added:


   \\HKEY_LOCAL_MACHINE\Software\Microsoft\Jet\3.5\engines\SandboxMode

For additional information about how to obtain the Microsoft Jet 3.5 SP3 update, please click the article number below to view the article in the Microsoft Knowledge Base:

Q172733 Updated Version of Microsoft Jet 3.5 Available on MSL

To make your system more resistant to malicious attacks while at the same time making it possible for older applications to keep running, the operation of the Sandbox box mode has changed in the Jet update so that it is fully under your control.

You can set the key to the following values, with 0 (zero) being most permissive and 3 being least permissive:

Setting	Description
0	Sandbox mode is disabled at all times.
1	Sandbox mode is used for Access applications, but not for non-Access Applications.
2	Sandbox mode is used for non-Access applications, but not for Access Applications. (This is the default value.)
3	Sandbox mode is used at all times.

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

With Sandbox mode enabled, if you try to use Visual Basic for Applications functions in a Jet query that are not considered safe, you receive the following error message:

JET_errExprUnknownFunction

Sandbox Mode Operations Allowed

The following is a list of functions that you can use in Jet queries when Sandbox mode is enabled. Any functions that do not appear in the list are not available in Sandbox mode.

ABS	array	ASC	ASCB	ASCW	ATN
CBOOL	CBYTE	CCUR	CDATE	CDBL	choose
CHR	CHR$	CHRB	CHRB$	CHRW	CHRW$
CINT	CLNG	COS	CSNG	CSTR	CVAR
CvDate	CVErr	date	DATE$	DATEADD	dateDiff
datePart	DATESERIAL	DATEVALUE	day	DdDB	error
error$	EXP	fix	format	format$	fv
hex	hex$	HOUR	IIF	IMEStatus	inStr
INT	IPMT	IRR	isDate	isEmpty	ISERROR
isNull	isNumeric	isObject	lCase	lCase$	LEFT
LEFT$	LEFTB	LEFTB$	LEN	LENB	LOG
lTrim	lTrim$	MID	MID$	MIDB	MIDB$
MINUTE	MIRR	MONTH	NOW	NPER	NPV
oct	oct$	partition	PMT	PPMT	PV
QBColor	RATE	RGB	RIGHT	RIGHT$	RIGHTB
RIGHTB$	rnd	round	rTrim	rTrim$	SECOND
sgn	SIN	SLN	space	space$	sqr
str	str$	strComp	strConv	string	string$
switch	SYD	TAN	TIME	TIME$	timer
timeSerial	TIMEVALUE	TRIM	TRIM$	typeName	uCase
uCase$	val	varType	WEEKDAY	YEAR

Additional query words: pra

Keywords : kbdta
Version : WINDOWS:3.5,7.0,97
Platform : WINDOWS
Issue type : kbbug