DoS via WebSocket frame with oversize 64-bit payload length field (Int trap in WebSocketFrameDecoder)

Summary

WebSocketFrameDecoder used Swift's trapping Int(_:) initializer to convert the 8-byte extended payload length field of a WebSocket frame (RFC 6455 §5.2). Any 64-bit length value with the most-significant bit set (≥ 0x8000_0000_0000_0000) caused a fatal runtime trap and terminated the process. The trap fired before maxFrameSize validation, so no configuration could mitigate it, and ByteToMessageDecoder cannot catch a runtime trap.

Impact

An unauthenticated remote peer can crash any NIOWebSocket-based server (including Vapor and Hummingbird) with a single 11-byte frame sent after a completed WebSocket handshake, dropping all active connections until the process restarts.

Proof of Concept

`

81 7F 80 00 00 00 00 00 00 00 00

`

Fix

Fixed in #3603: the decoder now uses Int(exactly:) and throws NIOWebSocketError.invalidFrameLength for out-of-range lengths instead of trapping.

Found & Fixed by @g0w6y