Have you identified what machine is sending these SYN packets (ip 10.0.0.1)? I have heard of some applications trying to initiate several connections at a time. Have you introduced any new machines/PC to the network recently? How long have you been seeing these messages?
I would first of all protect your network against SYN flood attacks as your network is currently wide open, given the configuration you posted. The following config will help minimize your exposure to a SYN flood attack.
set connection conn-max 100
set connection embryonic-conn-max 200
set connection per-client-embryonic-max 7
set connection per-client-max 5
set connection random-sequence-number enable
set connection timeout embryonic 0:0:45
The below link goes more in depth on attack mitigation and might be worth you reading.
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...