An issue was discovered in Suricata before 6.0.4. It is possible to bypass/evade any HTTP-based signature by faking an RST TCP packet with random TCP options of the md5header from the client side. After the three-way handshake, it's possible to inject an RST ACK with a random TCP md5header option. Then, the client can send an HTTP GET request with a forbidden URL. The server will ignore the RST ACK and send the response HTTP packet for the client's request. These packets will not trigger a Suricata reject action.
https://redmine.openinfosecfoundation.org/issues/4710
https://github.com/OISF/suricata/releases
https://github.com/OISF/suricata/commit/50e2b973eeec7172991bf8f544ab06fb782b97df
https://forum.suricata.io/t/suricata-6-0-4-and-5-0-8-released/1942