Vulnerability Development mailing list archives

Re: Plain text files in internet explorer


From: Eric Rostetter <eric.rostetter () physics utexas edu>
Date: Mon, 2 Sep 2002 22:11:23 -0500

Quoting Dan Kaminsky <dan () doxpara com>:

Mozilla will occasionally render downloads from a scripted backend as
plain text.  It's really pretty annoying, correct behavior or not.

Granted.  And the solution is to either fix the backend (best) or prompt
the user if they would like to take a non-standard action.
 
All things being equal, I'll go with correct behavior being first that
which matches what is presented to the user in the title bar, using
standard (Microsoftian!) in-band filename notation, then if nothing
usable is there, use the MIME-type as a hint.  In such a circumstance:

This is just plain wrong.  Just because it works for microsoft users
doesn't mean it works for the rest of the world.  At least until microsoft
really does take over the world and the rest of us go away.

foobar.txt is always read as text.

Okay.  So what is foobar.text read as?

foobar.html is always read as html.

But what if I don't want it read as html?

foobar.php and foobar.php, which really *should* be foobar.html because
-- dear god, they contain html -- can use the MIME-type to hint
themselves into HTML parsing.

But what if -- dear god -- it contains php and not html?

foobar.gif is always read as gif.

Okay.

a javascript virus is always obviously either javascript(foo.js) or
parsed as a gif(foo.gif).

But what if I don't want it parsed at all?

Importantly, I cannot concieve of a circumstance in which this can be
described incorrect behavior.

Okay, here's the crux of the problem.  Microsoft MSIE thinks that when a web
page wants to download a file called sample.com it must be an Microsoft (DOS)
executable and tries to execute it as such, even though I told it that it
was a text/plain or application/octet-stream file.  The problem is, it is
really a OpenVMS command file, which is a text/plain file, or at best
an OpenVMS executable, and Microsoft/MSIE file.  So executing it (which MSIE
does) is not only inappropriate/undesirable, but it could be totally 
disasterous!

Same for Microsoft thinking that *.doc is a word document, when other 
operating systems have been using *.doc for other purposes for years.
Same for *.dir, *.exe, etc.

Point is, not all OS platforms use the same file extensions, so if one decides
to force its file extensions on the user, it will cause problems with people
who use multiple OS platforms.

to view the previous format, not the latter.  GIFs can't exploit your
system.  Flash files can, just like any executable.

That is pure fud.
 
We're seeing a reasonably steady stream of "x posing as y to get around
z restriction" attacks made available specifically because filetype
handling is being hidden behind a user-opaque format standard that
places the type of a file far outside the file itself.

So?  How is this different that the exploits/viruses/restriction-bypasses
by using filename extensions (like something.xls.txt or something.exe.txt)?

I expect the exploit stream will eventually lead to MIME-type
deprecation. 

I seriously doubt it.  And it surely won't be replaced by file extensions
which suffer most all the same problems and additional problems also.

Yours Truly,

    Dan Kaminsky
    DoxPara Research
    http://www.doxpara.com


-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

"TAD (Technology Attachment Disorder) is an unshakable, impractical devotion
to a brand, platform, product line, or programming language. It's relatively
harmless among the rank and file, but when management is afflicted the damage
can be measured in dollars. It's also contagious -- someone with sufficient
political clout can infect an entire organization."

--"Enterprise Strategies" columnist Tom Yager.


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