WebSockets ws library for Node.js is vulnerable to a denial of service, caused by a regular expression denial of service (ReDOS) flaw in the in Sec-Websocket-Protocol header. By sending a specially-crafted regex input, a remote attacker could exploit this vulnerability to cause a slow down on the ws server, and results in a denial of service condition.

A vulnerability was found in the ping functionality of the ws module before 1.0.0 which allowed clients to allocate memory by sending a ping frame. The ping functionality by default responds with a pong frame and the previously given payload of the ping frame. This is exactly what you expect, but internally ws always transforms all data that we need to send to a Buffer instance and that is where the vulnerability existed. ws didn't do any checks for the type of data it was sending. With buffers in node when you allocate it when a number instead of a string it will allocate the amount of bytes.

ws is a "simple to use, blazing fast and thoroughly tested websocket client, server and console for node.js, up-to-date against RFC-6455". By sending an overly long websocket payload to a ws server, it is possible to crash the node process. This affects ws 1.1.0 and earlier.