Jansson, possibly 2.4 and earlier, does not restrict the ability to trigger hash collisions predictably, which allows context-dependent attackers to cause a denial of service (CPU consumption) via a crafted JSON document.
https://github.com/akheron/jansson/commit/8f80c2d83808150724d31793e6ade92749b1faa4
https://bugzilla.redhat.com/show_bug.cgi?id=1035538
http://lists.opensuse.org/opensuse-updates/2014-03/msg00057.html
http://comments.gmane.org/gmane.comp.security.oss.general/12099