The ASN.1 parser in strongSwan before 5.5.3 improperly handles CHOICE types when the x509 plugin is enabled, which allows remote attackers to cause a denial of service (infinite loop) via a crafted certificate.
https://www.strongswan.org/blog/2017/05/30/strongswan-vulnerability-%28cve-2017-9023%29.html
http://www.ubuntu.com/usn/USN-3301-1