The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.

Varnish 3.x before 3.0.7, when used in certain stacked installations, allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via a header line terminated by a \r (carriage return) character in conjunction with multiple Content-Length headers in an HTTP request.