full-disclosure - Re: DLL hijacking with Autorun on a USB drive

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Date: Tue, 31 Aug 2010 14:15:19 -0700
From: Dan Kaminsky <dan@...para.com>
To: Charles Morris <cmorris@...odu.edu>
Cc: "full-disclosure@...ts.grok.org.uk" <full-disclosure@...ts.grok.org.uk>,
	"paul.szabo@...ney.edu.au" <paul.szabo@...ney.edu.au>
Subject: Re: DLL hijacking with Autorun on a USB drive

On Aug 31, 2010, at 2:01 PM, Charles Morris <cmorris@...odu.edu> wrote:

>>
>>> ... Don't run applications from untrusted locations ...
>>
>> You got it wrong. Only trusted applications are run. - The attacker
>> prepares a WORD.DOC (and a RICHED20.DLL) file in some place. The
>> victim clicks on the WORD.DOC file, using his own installed MSWord.
>>
>
> Aaah, well if that is the issue, it seems to me that the  
> vulnerability here is
> that the application in question (MSWord) has it's CWD set to the  
> directory of
> the file that it is opening through the explorer shell.
>
> It should chdir() to it's own parent directory before doing anything  
> interesting
> that depends on CWD. (i.e. loading DLLs or executing "./ 
> amazingApp.sh")
>
> It's general good programming practice to be mindful of your CWD, I  
> know
> that personally; a call to chdir() is almost always at the top of my  
> script.
>
> So, I take back what I said about it being a non-issue, it IS in fact
> a vulnerability in the application.
>

Again, the clicker can't differentiate word (the document) from word  
(the executable).  The clicker also can't differentiate word (the  
document) from word (the code equivalent script).

The security model people keep presuming exists, doesn't.

Even the situation whereby a dll is dropped into a directory of  
documents -- the closest to a real exploit path there is -- all those  
docs can be repacked into executables.

> Cheers,
> Charles
>
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