TCP.Split.Handshake type alert

[Nikhil_lavate87]

Message meets Alert condition

The following intrusion was observed: TCP.Split.Handshake.

date=2018-10-23 time=18:00:56 devname=FG200D3916815028 devid=FG200D3916815028 logid=0419016384 type=utm subtype=ips eventtype=signature level=alert vd=root severity=medium srcip=23.234.39.77 srccountry="United States" dstip=172.16.10.38 srcintf="wan1" dstintf="port16" policyid=13 sessionid=71453405 action=detected proto=6 service="ca.vsign.in_http" attack="TCP.Split.Handshake" srcport=13633 dstport=8999 direction=outgoing attackid=26339 profile="all_default" ref="http://www.fortinet.com/ids/VID26339" incidentserialno=257015217 msg="a-ipdf: TCP.Split.Handshake, TCP split handshake at state: ESTABLISHED" crscore=10 crlevel=medium  

[tanr]

What's your question? 

Per the link, this is a protocol anomaly often used as an attack or for recon.

Per the log you posted you have it set to detect but not block. 

You may want to update your IPS Security Profile to block anomalies like this.