TL;DR; https://reviews.freebsd.org/D13869 For CentOS 6 the nss rpm contained nss-pam, however for CentOS 7 it was split out into a separate rpm. Add it to the port for consistency. Upstream patched the nss security vulnerability a few rpm versions ago, teach vuxml about this.
A commit references this bug: Author: tijl Date: Mon Jan 29 21:17:39 UTC 2018 New revision: 460338 URL: https://svnweb.freebsd.org/changeset/ports/460338 Log: Update range for linux-*-nss. PR: 225541 Submitted by: dbn Security: https://access.redhat.com/errata/RHSA-2017:2832 Changes: head/security/vuxml/vuln.xml
A commit references this bug: Author: tijl Date: Mon Jan 29 21:42:08 UTC 2018 New revision: 460341 URL: https://svnweb.freebsd.org/changeset/ports/460341 Log: Add back libnsspem. It was split off into a separate package. PR: 225541 Submitted by: dbn Changes: head/security/linux-c7-nss/Makefile head/security/linux-c7-nss/distinfo head/security/linux-c7-nss/pkg-plist.amd64 head/security/linux-c7-nss/pkg-plist.i386