RE: Manipulate PDFs with Malware

  If I recall correctly the structure of PDF files, elements contained in the file are easily overridden by appending a new value for the (specified) element.  So the challenges really are (a) to identify the element to be overridden (and if this is a form, the attacker might only have to do that once for all instances of that form...), and (b) possibly, to hide the fact that the size of the file as opened is slightly larger than the size advertised by the host it was downloaded from.
  Tricky, perhaps, and I don't actually know of malware that does this -- but it doesn't sound impossible to me.

David Gillett
CISSP CCNP


-----Original Message-----
From: Nick Clark [mailto:[email protected]] 
Sent: Sunday, January 20, 2013 22:55
To: Andre Silaghi
Cc: [email protected]
Subject: Re: Manipulate PDFs with Malware

Depends on how the PDF is formed. If they are just using an image or flat text, I cannot think of any easy way to do this. If they are using a form, and this barcode has a set attribute field, then you could probably search for the field and replace it with whatever you'd like to. 

---
Nick Clark

On Jan 19, 2013, at 10:59 PM, Andre Silaghi <[email protected]> wrote:

> Hello everybody,
> 
> Let me just explain to you a scenario before I ask my question about 
> it. You are starting to download a PDF file including a barcode which 
> is used to identify some payment information like the ammount of money 
> you have to pay and the receiver, maybe identified by another sequence 
> which is included.
> 
> Would it be possible to manipulate this barcode easily before or 
> during the opening process of the PDF in order to change the payment 
> information in a way that the attacker's information is encoded there?
> 
> Have you any experience with malware like this?
> 
> Best regards,
> André
> 
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