A flaw was found in Netty's HttpServerCodec. A remote, unauthenticated attacker can exploit this vulnerability by pipelining HTTP/1.1 requests on a single connection and withholding reads. This action causes the methodOverflowQueue to grow without limit, leading to unbounded heap memory consumption and a denial of service due to memory exhaustion.
https://github.com/netty/netty/releases/tag/netty-4.2.18.Final
https://github.com/netty/netty/releases/tag/netty-4.1.138.Final