The tokenizer in QPDF 6.0.0 and 7.0.b1 is recursive for arrays and dictionaries, which allows remote attackers to cause a denial of service (stack consumption and segmentation fault) or possibly have unspecified other impact via a PDF document with a deep data structure, as demonstrated by a crash in QPDFObjectHandle::parseInternal in libqpdf/QPDFObjectHandle.cc.
I just tested versions 5.1.1-r1 and 5.1.3-r1, they both return segmentation faults.
This bug has been fixed in the new 7.0.0 release:
2017-08-25 Jay Berkenbilt <email@example.com>
* Re-implement parser iteratively to avoid stack overflow on very
deeply nested arrays and dictionaries. Fixes #146.
@ Maintainer(s): Please advise how you would like to proceed.
GLSA Vote: No
cleanup will be tracked in bug #647776