A libreswan bugfix update has been released for CentOS 6.

CentOS Errata and Bugfix Advisory 2020:0257

Upstream details at :   https://access.redhat.com/errata/RHBA-2020:0257

The following updated files have been uploaded and are currently
syncing to the mirrors: ( sha256sum Filename )

i386:
2d6bf8c42bfd0e04076fe42afed24d4456f524ee09d17e32271381f6c7994534 libreswan-3.15-9.el6_10.i686.rpm

x86_64:
9bd9727a83f41e02e646e6a09f7546aba913f2ed4570d208af00d41833771a6f libreswan-3.15-9.el6_10.x86_64.rpm

Source:
1a68b8f2f23b1f53e13e9e62fe0f8d152f49adb12df8aa12dbf29209d426dcf1 libreswan-3.15-9.el6_10.src.rpm