The ikev2parent_inI1outR1 function in pluto/ikev2_parent.c in libreswan before 3.7 allows remote attackers to cause a denial of service (restart) via an IKEv2 I1 notification without a KE payload.
http://secunia.com/advisories/56276
http://secunia.com/advisories/56915
https://github.com/libreswan/libreswan/commit/2899351224fe2940aec37d7656e1e392c0fe07f0