Openswan versions 2.6.20 and below and Strongswan versions 4.2.13 and below suffer from a Dead Peer Detection denial of service vulnerability.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/76179/swan-dos.txt
Source: https://packetstormsecurity.com/files/76179/Openswan-Strongswan-Denial-Of-Service.html