programs/pluto/ikev1.c in libreswan before 3.17 retransmits in initial-responder states, which allows remote attackers to cause a denial of service (traffic amplification) via a spoofed UDP packet. NOTE: the original behavior complies with the IKEv1 protocol, but has a required security update from the libreswan vendor; as of 2016-06-10, it is expected that several other IKEv1 implementations will have vendor-required security updates, with separate CVE IDs assigned to each.
https://lists.libreswan.org/pipermail/swan-dev/2016-March/001394.html
https://github.com/libreswan/libreswan/commit/152d6d95632d8b9477c170f1de99bcd86d7fb1d6