If you don't have a current licnese on the sensor (you can verify in the output of the same "show version" command) you can still apply software updates to the sensor. Each software update contains the latest signature pack as of their release date.
Although this may keep you running updated signatures (on a less frequent basis that regular signature updates) the newly released signatures in the software updates contain the "first attempt" signatures utilizing new signature engines and are a little more buggy than the typical signature update.
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...
Table of Contents 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 an...