This indicates an attack on a denial of service vulnerability in Openswan.
The vulnerability is caused by an error when the vulnerable software handles a malicious DPD packet. It allows a remote attacker to crash the pluto daemon.
Openswan and Strongswan IPsec 2.6 before 2.6.21 and 2.4 before 2.4.14, and Strongswan 4.2 before 4.2.14 and 2.8 before 2.8.9
Denial of Service
Upgrade to a latest version, or apply the appropriate patch as listed at http://www.openswan.org/CVE-2009-0790/