The ZlibDecoders in Netty 4.1.x before 4.1.46 allow for unbounded memory allocation while decoding a ZlibEncoded byte stream. An attacker could send a large ZlibEncoded byte stream to the Netty server, forcing the server to allocate all of its free memory to a single decoder.
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.