A stack-consumption vulnerability was found in libqpdf in QPDF 6.0.0, which allows attackers to cause a denial of service via a crafted file, related to the PointerHolder function in PointerHolder.hh, aka an "infinite loop."
https://usn.ubuntu.com/3638-1/
https://github.com/qpdf/qpdf/issues/118
https://euvd.enisa.europa.eu/vulnerability/EUVD-2017-3239
http://somevulnsofadlab.blogspot.jp/2017/07/qpdfan-infinite-loop-in-libqpdf_21.html