Re: Securing file access

[Joseph Miller <joseph () tidetamerboatlifts com>]

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Would it be possible to change the content type on the server side to a 
generic binary file to prevent acrobat reader from loading in the plugin 
mode?  If it is possible, then Windows would ask the user to open the file, 
the PDF extension would be found, and the file would open externally.

- -Joseph


On Thursday 30 September 2004 6:15 pm, Calderon, Juan Carlos (GE Commercial 
Finance, NonGE) wrote:
> woah!
>
> Sending a path in a hidden field to remove a file in server doesn't sound
> good to me.  be carefull with this approach!
>
>
> -----Original Message-----
> From: Beckner, Chad A [mailto:cbeckner () iupui edu]
> Sent: Miércoles, 29 de Septiembre de 2004 09:09 p.m.
> To: Shields, Larry; webappsec () securityfocus com
> Subject: RE: Securing file access
>
>
> You could also copy the file to a temporary read-only directory, and run
> an administrative script to clean out the temp directory every night,
> hour, or even after the user has received the file (i.e. on the next
> page hit using a hidden variable, such as "remove_file",
> value="adobe.pdf").
>
> - Chad
>
> -----Original Message-----
> From: Shields, Larry [mailto:Larry.Shields () FMR COM]
> Sent: Wednesday, September 29, 2004 1:16 PM
> To: webappsec () securityfocus com
> Subject: RE: Securing file access
>
>
>       Be aware that the acrobat reader if using the IE browser plug-in
> viewer has been known to have problems when using this method to send
> PDF files.  We have seen common problems where users ended up with blank
> documents or received errors about the PDF file not being correct.  From
> what I've seen, the two solutions if you can't have this possible
> failure are to either a) make customers all change their acrobat reader
> configuration to start in "helper" mode (meaning kick off acrobat
> external to the browser plug-in) or b) store things on the file system
> and redirect the user to the PDF file.  Option b does have issues to
> make sure it is done securely of course, such as clean-up of old files,
> making sure that file names cannot be guessed or predicted by other
> users, and that there is no potential for file naming collisions between
> users.
>
> -Larry
>
>
> -----Original Message-----
> From: Ian [mailto:webappsec2 () fishnet co uk]
> Sent: Tuesday, September 28, 2004 5:05 AM
> To: John M. L.; webappsec () securityfocus com
> Subject: Re: Securing file access
>
> On 27 Sep 2004 at 11:57, John M. L. wrote:
> > I have a project that involves a members only area on web page on IIS.
> > The members' only area is secured by a database (MS Access) so users
> > are authenticated by their name and some MD5 hash etc.  I need to
> > allow files (mostly PDFs) for download to authenticated users only.
> > In my opinion this means that the files can not be stored in any www
> > accessible folder (regardless of any renaming convention etc, I
> > absolutely cannot have someone guess a file name to download).  In
> > order to access the files, the database would link a file to a unique
> > id, so a page that validates the user would then give access to the
> > file stored outside of the www on the server.  Now, this is where the
> > real question lies.  How is this possible since the files are not in a
>
> www accessible path, since a mere link to a file won't due.
>
> > Any thoughts would be welcome.  If I'm going about this completely
> > wrong that would be nice to no too :)  Forgive me if the answer is
> > simple, I'm a Linux fan and haven't used IIS etc for years.
> > One more note: IIS, MS Access and VBScript are not my technologies of
> > choice, but merely what I was given to work with.  I also have very
> > limited control over administering IIS.
> >
> > John
> > www.recaffeinated.com
>
> Hi John,
>
> You are going about this the right way.
>
> Store the PDFs outside the www root, but still give the user
> ISR_<computer name> permission to read the files ( or whatever user your
> site is running under).  Once the web user has authenticated, your
> script can read the PDF into memory then stream the file to the user.  A
> simple example is below:
>
> <%
>
> set fs=server.createobject("Scripting.filesystem")
>
> set PDFin=fs.opentextfile(pathtoPDF,1,false)
> PDF=PDFin.readall
> PDFin.close
> set PDFin=nothing
>
> Response.contenttype="application/pdf"
>
> resonse.binarywrite StrToBin(PDF)
>
> response.end
>
> function StrToBin(str)
>       for x=1 to Len(str)
>               StrToBin=StrToBin & ChrB(Asc(Mid(str,x,1)))
>       next
> end function
>
> %>
>
> You may not need to use the StrToBin function - I can't remember off the
> top of my
> head ;)
>
> Regards
>
> Ian
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