Didier Stevens

Monday 9 November 2009

Quickpost: “Hiding” a PDF Document

Filed under: Entertainment,My Software,PDF,Quickpost — Didier Stevens @ 15:00

Here’s some Python code (it uses my mPDF module) to append a new PDF document to an existing PDF document to “hide” the original document. Recovering the original is trivial, you open the PDF document with a HEX-editor and delete the appended document (starting after the second %%EOF counting from the end of the file). This trick uses incremental updates.

20091107-172245

#!/usr/bin/python

__description__ = 'make-pdf-hide-original, use it to "hide" the original PDF document'
__author__ = 'Didier Stevens'
__version__ = '0.0.1'
__date__ = '2009/11/07'

"""
Source code put in public domain by Didier Stevens, no Copyright

https://DidierStevens.com

Use at your own risk

History:
 2009/11/07: start

Todo:

"""

import mPDF
import time
import zlib
import optparse

def Main():
    oParser = optparse.OptionParser(usage='usage: %prog [options] pdf-file\n' + __description__, version='%prog ' + __version__)
    oParser.add_option('-s', '--line', default='Hello World', help='The line of text to print on the screen (default Hello World')
    (options, args) = oParser.parse_args()

    if len(args) != 1:
        oParser.print_help()
        print ''
        print '  %s' % __description__
        print '  Source code put in the public domain by Didier Stevens, no Copyright'
        print '  Use at your own risk'
        print '  https://DidierStevens.com'

    else:
        pdffile = args[0]
        oPDF = mPDF.cPDF(pdffile)
        oPDF.template1()
        oPDF.stream(5, 0, 'BT /F1 24 Tf 100 700 Td (%s) Tj ET' % options.line)
        oPDF.xrefAndTrailer('1 0 R')

if __name__ == '__main__':
   Main()

Quickpost info

 


3 Comments »

  1. Really cool and creative but this can be misused by bad guys in hiding the original pdf with dodgy obfuscated javascript with exploits.

    Comment by Jag — Monday 9 November 2009 @ 21:19

  2. [...] Quickpost: “Hiding” a PDF Document – didierstevens.com Using incremental updates, you can hide a PDF inside a PDF. Cause we heard you liked PDFs, dawg. [...]

    Pingback by Week 46 in Review – 2009 | Infosec Events — Wednesday 13 January 2010 @ 6:02

  3. [...] Tags: tiff While analyzing a recent pdf sample exploiting the TIFF vuln it used a known technique to obfuscate it’s content: it appends a pdf to the first one after a bunch of of [...]

    Pingback by PDF CVE-2010-0188 « inREVERSE — Saturday 24 April 2010 @ 13:32


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