Q232449: Sample ASP Code May be Used to View Unsecured Server Files
Article: Q232449
Product(s): Internet Information Server
Version(s): winnt:4.0
Operating System(s):
Keyword(s):
Last Modified: 06-AUG-2002
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The information in this article applies to:
- Microsoft Internet Information Server version 4.0
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SYMPTOMS
========
When you install the following Active Server Page (ASP) sample files on a
computer running Internet Information Server (IIS) 4.0, a Web visitor may be
able to use these files to gain access to and read any known file on the same
logical disk as the installed ASP code, which is not protected by setting the
system Access Control Lists (ACLs) for these files:
- <IIS_DIRECTORY>\Iissamples\Exair\Howitworks\Code.asp
- <IIS_DIRECTORY>\Iissamples\Exair\Howitworks\Codebrws.asp
- <IIS_DIRECTORY>\Iissamples\Sdk\Asp\Docs\Codebrws.asp
- <Program_Files>\<Common_Files>\System\Msadc\Samples\Selector\Showcode.asp
Please note, however, that the Web visitor cannot change, delete, or add any
files.
CAUSE
=====
The installed ASP code was never intended for anything other than demonstration
purposes and does not restrict which files a visitor to a Web site can view.
WORKAROUND
==========
Remove all copies of Showcode.asp, Code.asp, and CodeBrws.asp from the
production server, or set the ACLs for each of these files so that only the
appropriate users have access.
NOTE: Per normal security practices, the ACLs on the server should always be set
to enable Web visitors to view only the files they need, and to deny access to
all others.
RESOLUTION
==========
A supported fix is now available from Microsoft, but it is only intended to
correct the problem that is described in this article. Apply it only to systems
that are experiencing this specific problem.
To resolve this problem, contact Microsoft Product Support Services to obtain the
fix. For a complete list of Microsoft Product Support Services phone numbers and
information about support costs, visit the following Microsoft Web site:
http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS
NOTE: In special cases, charges that are ordinarily incurred for support calls
may be canceled if a Microsoft Support Professional determines that a specific
update will resolve your problem. The usual support costs will apply to
additional support questions and issues that do not qualify for the specific
update in question.
The English version of this fix should have the following file attributes or
later:
Date Time Size File name Platform
-------------------------------------------------------------------------
5/17/99 1:17PM 3Kb Code.asp <x86>
5/17/99 1:17PM 8Kb Codebrw1.asp <x86>
5/17/99 1:17PM 8Kb Codebrw2.asp <x86>
5/17/99 1:17PM 6Kb Showcode.asp <x86>
5/17/99 1:17PM 3Kb Code.asp <alpha>
5/17/99 1:17PM 8Kb Codebrw1.asp <alpha>
5/17/99 1:17PM 8Kb CodeBrw2.asp <alpha>
5/17/99 1:17PM 6Kb Showcode.asp <alpha>
This hotfix has been posted to the following Internet location as Fix2450I.exe
(Intel) or Fix2450A.exe (Alpha):
ftp://ftp.microsoft.com/bussys/iis/iis-public/fixes/usa/Viewcode-fix/
STATUS
======
Microsoft has confirmed that this is a problem in Internet Information Server
4.0.
MORE INFORMATION
================
Microsoft highly recommends that customers evaluate the degree of risk that this
vulnerability poses to their systems and determine whether to download and
install the fix.
This fix corrects the vulnerability by restricting Showcode.asp, Code.asp, and
CodeBrws.asp to viewing only files in the current directory. However, Web site
operators who do not have a need to provide the file viewing capability may
choose to remove all copies OF Showcode.asp, Code.asp, and CodeBrws.asp from the
server altogether.
Environment in Which These ASP Files May Cause Security Risk
------------------------------------------------------------
Security exposure is limited to the situation in which all of the following
conditions are true:
- Servers have the sample sites installed.
- The sample sites are not protected by ACLs (Access Control Lists).
- Sensitive data exists on the same logical drive as Showcode.asp, Code.asp,
and CodeBrws.asp.
- Files containing sensitive data allow the "Everyone" user group read or
greater access in the ACL.
- Malicious users know the path and file name of files that contain sensitive
data.
Installing the Fix
------------------
The fix installation program (Fix2450I.exe [Intel] and Fix2450A.exe [Alpha])
automatically replaces existing Showcode.asp, Code.asp, and CodeBrws.asp files.
NOTE: The default installation directories listed below the fix installation
package will attempt to locate the files as they were installed onto the
effected system. After you install the fix, you should perform a complete disk
search for these files to verify that all instances of these files have been
replaced. If your IIS 4.0 installation was installed into a different directory
than the default directory, then you must verify that the effected files have
been removed and replaced by performing a full disk search for these files.
- <IIS_DIRECTORY>\Iissamples\Exair\Howitworks\Code.asp
- <IIS_DIRECTORY>\Iissamples\Exair\Howitworks\Codebrws.asp
- <IIS_DIRECTORY>\Iissamples\Sdk\Asp\docs\Codebrws.asp
- <Program_Files>\<Common_Files>\System\Msadc\Samples\Selector\Showcode.asp
A complete installation of the sample code for Internet Information Server 4.0
and the Internet SDK will install various copies of Showcode.asp, Code.asp, and
CodeBrws.asp in different directories. Therefore, if you to choose to remove it,
perform a full-disk search to locate all copies.
To manually extract the modified ASP files from the distribution fix, do the
following:
1. Copy the distribution file (Fix2450I or Fix2450A as appropriate) to a
temporary location.
2. Open a command prompt and change to that directory.
3. On the command line type "Fix2450I.EXE /T:c:\temp /C" or "Fix2450A.EXE
/T:c:\temp /C" as appropriate. This command will extract the files to the
location of c:\temp.
4. Various installation files will be extracted, but the effected files are as
follows:
- Code.asp (this file is installed in the %Program Files%\Microsoft Visual
Studio\VIntDev98\Sample\Gallery\content directory)
- CODEBRW1.ASP (this file is installed in the \iissamples\ExAir\HowItWorks
directory)
- CODEBRW2.ASP (this file is installed in the \Iissamples\Sdk\asp\Docs\
directory)
- Showcode.asp
NOTE: Showcode.asp, Code.asp, and CodeBrws.asp should always have the ACL
permissions set to Administrators only, or to a group that is limited to Web
content developers.
Please note that you may have to extract and copy the files manually if the hot
fix installation will not complete.
IMPORTANT NOTE: The Codebrws.asp file has the same name in both of the target
directories. However, for the purpose of the hot fix, it is given different
names so that they are differentiated. The hot fix installer will rename place
and rename them appropriately. If you manually install them, however, you will
need to rename them appropriately.
Code Changes in the Fix
-----------------------
Showcode.asp, Code.asp, and CodeBrws.asp files use "server.mappath" without any
restrictions on what is passed to this function. Because Showcode.asp, Code.asp,
and CodeBrws.asp allow a user to enter a path and filename, a malicious user
could gain access to and read (read-only) any known file on the same logical
disk as Showcode.asp, Code.asp, and CodeBrws.asp, which are not protected (no
ACLs set).
The code added to Code.asp is as follows:
(Note: These lines of code may wrap):
<SCRIPT LANGUAGE=VBScript RUNAT=Server>
REM **************************************
REM intended behavior:
REM allow access to only .asp, .htm, .html, .inc files
REM in some directory starting from /IISSAMPLES
REM and without .. in the path
REM **************************************
FUNCTION fValidPath (ByVal strPath)
If InStr(1, strPath, "/iissamples/", 1) Then
' the beginning of the string looks good
Dim dwLen
Dim SomeKnownExtension
SomeKnownExtension = false
dwLen = Len(strPath)
If Not SomeKnownExtension Then
If InStr(dwLen-5,strPath,".html",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".htm",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".asp",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".inc",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
fValidPath = 0
Exit Function
End If
' now the most important part: look for ..
If InStr(1,strPath,"..",1) Then
fValidPath = 0
Else
fValidPath = 1
End If
Else
fValidPath = 0
End If
END FUNCTION
</SCRIPT>
The following code was removed from Code.asp:
(Note: These lines of code may wrap):
< ' Function to determine if a file exists
Function FileExists(Source)
On Error Resume Next
strFilename = Server.MapPath(Source)
Set FileObject = Server.CreateObject("Scripting.FileSystemObject")
FileExists = False
' Attempt to open the file
Set oTempStream = FileObject.OpenTextFile(strFilename, 1, FALSE, TRUE )
If Err = 0 Then FileExists = True
End Function
%>
The following code was added to ShowCode.asp
(Note: These lines of code may wrap):
REM *************** NOTICE ****************
REM * This file may only be used to view *
REM * source code of .asp files in the *
REM * AdvWorks or ASP Sample directory. *
REM * If you wish to change the security *
REM * on this, modify or remove this *
REM * function. *
REM ***************************************
REM **************************************
REM intended behavior:
REM allow access to only .asp, .htm, .html, .inc files
REM in some directory starting from /Msdac
REM and without .. in the path
REM **************************************
FUNCTION fValidPath (ByVal strPath)
If InStr(1, strPath, "/Msadc/", 1) Then
' the beginning of the string looks good
Dim dwLen
Dim SomeKnownExtension
SomeKnownExtension = false
dwLen = Len(strPath)
If Not SomeKnownExtension Then
If InStr(dwLen-5,strPath,".html",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".htm",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".asp",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".inc",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
fValidPath = 0
Exit Function
End If
' now the most importan part: look for ..
If InStr(1,strPath,"..",1) Then
fValidPath = 0
Else
fValidPath = 1
End If
Else
fValidPath = 0
End If
END FUNCTION
</SCRIPT>
The following code was added to CodeBrws.asp:
(Note: These lines of code may wrap):
REM **************************************
REM intended behavior:
REM allow access to only .asp, .htm, .html, .inc files
REM in some directory starting from /IISSAMPLES
REM and without .. in the path
REM **************************************
FUNCTION fValidPath (ByVal strPath)
If InStr(1, strPath, "/iissamples/", 1) Then
' the beginning of the string looks good
Dim dwLen
Dim SomeKnownExtension
SomeKnownExtension = false
dwLen = Len(strPath)
If Not SomeKnownExtension Then
If InStr(dwLen-5,strPath,".html",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".htm",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".asp",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
If InStr(dwLen-4,strPath,".inc",1) Then
SomeKnownExtension = true
End If
End If
If Not SomeKnownExtension Then
fValidPath = 0
Exit Function
End If
' now the most importan part: look for ..
If InStr(1,strPath,"..",1) Then
fValidPath = 0
Else
fValidPath = 1
End If
Else
fValidPath = 0
End If
END FUNCTION
</SCRIPT>
Purpose of Showcode.asp, Code.asp, and CodeBrws.asp, and Related MSDN Samples
-----------------------------------------------------------------------------
The purpose of Showcode.asp, Code.asp, and CodeBrws.asp. is to show the Web
content developer the code that makes the sample sites work. This type of
function is also used on the Web author's workshop on the MSDN site
(http://msdn.microsoft.com/workshop/c-frame.htm#/workshop/author/default.asp).
If you base your content on one of the sample sites, remove the buttons (links)
that load the code into Showcode.asp, Code.asp, and CodeBrws.asp to display it.
Installing Samples and Documentation on Production Servers
----------------------------------------------------------
Most Internet Information Server 4.0 users do not install the sample sites on
their production servers, just as they do not install the documentation. They
are not typically needed on the production servers, as they use additional disk
space. Because they are just samples, they may not be secure in a production
environment.
If you have a need to include the samples on a production server, consider
restricting access to your developers only.
Additional References
---------------------
For more information related to this issue, please see the following:
Microsoft Security Bulletin MS99-013, "Patch Available for ViewCode.asp
Vulnerability" (The Web-posted version of this bulletin),
http://www.microsoft.com/security/bulletins/ms99-013.asp
For additional security-related information about Microsoft products, please
visit:
http://www.microsoft.com/security
Additional query words: patch hotfix hot fix qfe default setup set up viewcode utility hacker breach read see source
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Keywords :
Technology : kbiisSearch kbiis400
Version : winnt:4.0
Hardware : ALPHA x86
Issue type : kbbug
Solution Type : kbfix
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