The ProcessMimeEntity function in util-decode-mime.c in Suricata 4.x before 4.0.6 allows remote attackers to cause a denial of service (segfault and daemon crash) via crafted input to the SMTP parser, as exploited in the wild in November 2018.

Suricata before 4.0.5 stops TCP stream inspection upon a TCP RST from a server. This allows detection bypass because Windows TCP clients proceed with normal processing of TCP data that arrives shortly after an RST (i.e., they act as if the RST had not yet been received).

An issue was discovered in Suricata before 3.1.2. If an ICMPv4 error packet is received as the first packet on a flow in the to_client direction, it confuses the rule grouping lookup logic. The toclient inspection will then continue with the wrong rule group. This can lead to missed detection.

Suricata before 4.0.4 is prone to an HTTP detection bypass vulnerability in detect.c and stream-tcp.c. If a malicious server breaks a normal TCP flow and sends data before the 3-way handshake is complete, then the data sent by the malicious server will be accepted by web clients such as a web browser or Linux CLI utilities, but ignored by Suricata IDS signatures. This mostly affects IDS signatures for the HTTP protocol and TCP stream content; signatures for TCP packets will inspect such network traffic as usual.