Insecure Features in PDFs

• qpdf

  18 3,052 9.5 C++

  QPDF: A content-preserving PDF document transformer

  

Given how well Preview.app and Safari work for viewing >99% of PDFs I actually encounter in the wild, this article makes Apple's engineering decisions look good.

It also confirms many suspicions I've had over the years that have led me to, e.g., running all PDFs from questionable sources through VirusTotal before viewing on platforms where I wouldn't normally run antivirus software.

The original article also confirms my suspicions that this step is inadequate:

Because the Launch action can be considered as a danger- ous feature, we conducted a large-scale evaluation of 294,586 PDF documents downloaded from the Internet, in order to research if there are any legitimate use cases at all. Of those documents, only 532 files (0.18%) contained a Launch action. While none of the files was classified as malicious according to the VirusTotal database, we conclude that the Launch action is rarely used in the wild and its support should be removed by PDF implementations as well as the standard.

Incidentally, the Launch action is still present in the most recent version of the PDF standard[1], with only OS-specific launch parameters deprecated (which include passing arguments to the launched executable, so eliminating the deprecated feature is still a significant security gain).

Finally, I'm both personally and professionally curious about how the non-DoS examples in this articles may apply to non-viewer PDF tools and libraries like qpdf[2] and Ghostscript's original and recently reimplemented PDF interpreters[3].

[1] https://pdfa.org/resource/iso-32000-pdf/

(registration required, but at least the base standard is available at no cost; sadly, important incorporated standards like ISO 21757-1:2020 [ECMAScript for PDF] are not)

[2] https://qpdf.sourceforge.io

[3] https://ghostscript.com/blog/pdfi.html

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