SDF, please!

Published: 2010-09-02
Last Updated: 2010-09-02 00:50:00 UTC
by Daniel Wesemann (Version: 1)
19 comment(s)

"We're under a targeted malware attack!", a friend of mine yelled into the phone. "We are getting lots of oddly named PDFs, attached to personalized emails, sent only to certain employees in our firm!". From some past experience with chewing through our nasty malware repository here at SANS ISC, I had learned a thing or two about malicious PDFs, so I agreed to take a look.

One hour later, it was clear that the PDFs in this case were free of any exploit, completely harmless, and contained only the average "I AM A COUSIN OF THE LATE ZESKEKE NGAGWENE" type of Nigerian 419 (advance-fee) fraud spam.

But the whole episode gave me pause. It really looks like the past two years of never ending new waves of PDF exploits have degraded PDF in the mind of every security analyst to a level somewhere at par with ANI and SCR files: No matter what it claims to be, it ain't nothing good.

I very much agree with Stephen Northcutt's comment in SANS Newsbites two months ago. He asked: "Is there an alternative to a .pdf? It was supposed to be a printable image of what you saw on the screen. At least that was the idea 15 years ago. It should not need "launch" functions to do that. Do you remember five or six years ago, you weren't supposed to send an excel spreadsheet or a word document because they might contain malware, you were supposed to send a .pdf. Guess that has changed!"

Time for SDF - the Safe Document Format. You know, one that just supports pixels in various shades of gray, and does not need to include the ability to play a movie in 3D accompanied by surround sound. Just a nice plain document that can be opened, read and printed, without any of the nagging feeling of dread that nowadays accompanies clicking on a PDF.

Anyone?

 

Keywords: pdf PDF exploit
19 comment(s)

Comments

We already have one; it is called ".JPG" (or ".GIF").
I'd be happy to see pdf die a quick death
Rather than worry about most exploits, I just disable most of the features by removing files in programfiles\Adobe\Reader 9.0\Reader\plug_ins. You can even modify the install package so upgrades don't put them back. If you do that and remove perms to authplay.dll (Flash) then Reader isn't *so* bad.

Maybe we could bring back PostScript, but that's turing-complete, and since they can't sandbox Reader I doubt they can sandbox PostScript.
Check out PDF/A format:
http://en.wikipedia.org/wiki/PDF/A
Also, PDF was always about more than "a printable image of what you saw on the screen.". The troubles really started when the singing and dancing extensions were added to later versions and software.

A valuable contribution to security would be an open source PDF reader that did not implement the dangerous stuff.

And Steve: Postscript has had very dangerous features (worse than Turing-completeness) for a long time. Doesn't mean they need to be implemented! SafePDF built on top of SafePostscript with sufficient backward compatibility ... One could hope.

A valuable contribution to security would be an open source PDF reader that did not implement the dangerous stuff.

And Steve: Postscript has had very dangerous features (worse than Turing-completeness) for a long time. Doesn't mean they need to be implemented! SafePDF built on top of SafePostscript with sufficient backward compatibility ... One could hope.
i like the pdf/a limitation idea, also png image but my alltime favorite is still ascii :')

its sad that one of the more reliable formats has been retooled to continuously add complexity. adobe reader is just gigantic lately lol.
How about DjVu (http://en.wikipedia.org/wiki/Djvu)?
A was thinking, what about multipage TIFF ? Our fax machine is sending dozens a day, and it does the job.
For important documents there is nothing wrong with using plain text. Various GIF/JPEG/TIFF libraries have suffered from buffer overflows, and any interpreted format will eventually be bastardized by the sales critters to be able to do singing/dancing 'Corporate Image' impressions. And the cycle starts again.
I wonder if anyone has done a study on how much use all the extra features get. How many PDFs actually have embedded multimedia? I've never seen one. 3D animations? Not here. Maybe if it could be demonstrated that no one cares, a lot of the cruft could be made optionally installable components, not part of the standard install.

@cynic, but how can I use Comic Sans in my important document if it's in plain text? :-)
How about text files? Plain text, formatted with line breaks, carriage returns, punctuation marks, and whitespace.

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