strongswan vulnerability

USN-6488-1 fixed a vulnerability in strongSwan. This update provides
the corresponding updates for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS.

Original advisory details:

Florian Picca discovered that strongSwan incorrectly handled certain DH
public values. A remote attacker could use this issue to cause strongSwan
to crash, resulting in a denial of service, or possibly execute arbitrary
code.