Is this an attack ?

Recently, I found a lot of entries like this in my /var/log/messages :

If yes, what kind of attack? They are not flooding btw.

Code: 
Jun 19 10:26:04 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=65.54.188.10 DST=66.96.21.1 LEN=48 TOS=0x00 PREC=0x00 TTL=118 ID=58769 DF PROTO=TCP SPT=5120 DPT=80 SEQ=1838627927 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B401010402)
Jun 19 10:26:10 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=65.54.188.10 DST=66.96.21.1 LEN=48 TOS=0x00 PREC=0x00 TTL=118 ID=63305 DF PROTO=TCP SPT=5120 DPT=80 SEQ=1838627927 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B401010402)
Jun 19 10:26:33 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=13250 PROTO=TCP SPT=1508 DPT=80 SEQ=450000740 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:26:33 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=13260 PROTO=TCP SPT=1510 DPT=80 SEQ=4140679922 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:26:33 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=13261 PROTO=TCP SPT=1511 DPT=80 SEQ=281826188 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:26:44 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=14225 PROTO=TCP SPT=1535 DPT=80 SEQ=8976595 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:26:44 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=14226 PROTO=TCP SPT=1536 DPT=80 SEQ=2610769637 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:26:44 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=14227 PROTO=TCP SPT=1537 DPT=80 SEQ=2566103807 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:27:33 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=18123 PROTO=TCP SPT=1635 DPT=80 SEQ=3825070604 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:27:33 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=18132 PROTO=TCP SPT=1636 DPT=80 SEQ=2880653807 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:27:50 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=19427 PROTO=TCP SPT=1643 DPT=80 SEQ=787092861 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:27:50 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=19428 PROTO=TCP SPT=1644 DPT=80 SEQ=1469738297 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:27:50 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=19429 PROTO=TCP SPT=1645 DPT=80 SEQ=2921777601 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:30:24 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=27777 PROTO=TCP SPT=1690 DPT=80 SEQ=3775268071 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:30:51 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=66.12.74.218 DST=66.96.21.1 LEN=60 TOS=0x00 PREC=0x00 TTL=120 ID=29261 PROTO=TCP SPT=1708 DPT=80 SEQ=2904218735 ACK=0 WINDOW=65535 RES=0x00 SYN URGP=0 OPT (020405B40101080A000000000000000001010402)
Jun 19 10:31:01 main kernel: ip_conntrack_tcp: INVALID: invalid SYN (ignored) SRC=82.116.147.89 DST=66.96.21.1 LEN=48 TOS=0x00 PREC=0x00 TTL=112 ID=56386 DF PROTO=TCP SPT=62001 DPT=80 SEQ=505986974 ACK=0 WINDOW=64240 RES=0x00 SYN URGP=0 OPT (0204055001010402)

 

 

 

 

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