In OISF LibHTP before 0.5.31, as used in Suricata 4.1.4 and other products, an HTTP protocol parsing error causes the http_header signature to not alert on a response with a single \r\n ending.
{ "availability": "No subscription required", "ubuntu_priority": "medium", "binaries": [ { "binary_name": "libhtp-dev", "binary_version": "1:0.5.31-1" }, { "binary_name": "libhtp2", "binary_version": "1:0.5.31-1" }, { "binary_name": "libhtp2-dbgsym", "binary_version": "1:0.5.31-1" } ] }