HTTP/2 zero-day vulnerability results in record-breaking DDoS attacks
tl;dr HTTP/2 allows clients to DDoS backends much more effectively by using the multiple-stream feature of HTTP/2 to amplify their attack directly inside the reverse proxy (which typically translates HTTP/2 to HTTP/1).> When Cloudflare's reverse proxies process incoming HTTP/2 client traffic, they copy the data from the connection’s socket into a buffer and process that buffered data in order. As each request is read (HEADERS and DATA frames) it is dispatched to an upstream service. When RST_STREAM frames are read, the local state for the request is torn down and the upstream is notified that the request has been canceled. Rinse and repeat until the entire buffer is consumed. However this logic can be abused: when a malicious client started sending an enormous chain of requests and resets at the start of a connection, our servers would eagerly read them all and create stress on the upstream servers to the point of being unable to process any new incoming request.