Are these PDF object's presence normal in all documents which use Acroforms or XFA forms?

Question

2 0 obj
<</XFA 1 0 R >>
endobj

3 0 obj
<<
  /Extensions
  <<
     /ADBE
     <<
        /ExtensionLevel 3
        /BaseVersion /1.7
     >>
   >>
   /AcroForm 2 0 R
   /Type /Catalog
   /Pages 4 0 R
   /NeedsRendering true
>>
endobj

Actually, I was analyzing a PDF with CVE-2013-2729 where a specially crafted RLE8 encoded bitmap image causes a integer overflow via the XFA component of Adobe Reader.

Also, what is the difference between an direct and indirect object in PDF ?I am always confused in these two.

Answer 1

First of all, these objects look completely innocent.

Secondly, the difference between direct and indirect objects is exactly what you would expect. If you look at the line:

<</XFA 1 0 R >>

That's the use of an indirect object. The object is defined elsewhere and in this dictionary it's referred to (indirected).

If you look at the line

/ExtensionLevel 3

That's the use of a direct object. The object is defined in place without indirection.