A major component of VRF security is path isolation. As the guide below states this isolation means that, "no communication between devices belonging to different VRFs is allowed unless explicitly configured."
However I would not rely upon it as your only security measure within your network.
The guide also discusses how to deploy this technology behind your firewall. Another excellent reference is the Cisco Validated Design for a Virtualised Multi-Tenant Data Centre that can be found here:
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
[toc:faq]Introduction:This document describes details on how NAT-T
works.Background:ESP encrypts all critical information, encapsulating
the entire inner TCP/UDP datagram within an ESP header. ESP is an IP
protocol in the same sense that TCP and UDP are I...