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 QPDFTokenizer::resolveLiteral function in QPDFTokenizer.cc after two consecutive calls to QPDFObjectHandle::parseInternal, aka an "infinite loop."
https://usn.ubuntu.com/3638-1/
https://github.com/qpdf/qpdf/issues/117
https://euvd.enisa.europa.eu/vulnerability/EUVD-2017-3236
http://somevulnsofadlab.blogspot.jp/2017/07/qpdfan-infinite-loop-in-libqpdf.html