Netty (io.netty:netty-codec-http) versions up to and including 4.1.137.Final and from 4.2.0.Final through 4.2.17.Final accept an unlimited number of concurrent remote-initiated SPDY streams: SpdySessionHandler defaults localConcurrentStreams to Integer.MAX_VALUE and exposes no API to change it. A remote peer that opens a SPDY connection and sends millions of SYN_STREAM frames with FLAG_FIN=0 causes the server to allocate unbounded heap and direct memory, eventually triggering a JVM OutOfMemoryError and crashing the service. Fixed in 4.1.138.Final and 4.2.18.Final.