A vulnerability in the ping functionality of ws module which allowed clients to allocate memory by simply sending a ping frame. The ping functionality by default responds with a pong frame and the previously given payload of the ping frame. As a result, client receives non-zeroed out allocated buffer from server of arbitrary length. Assuming the usage of modern kernel, only the memory previously used and deallocated by the node process and the memory that has been previously allocated as a Buffer can be leaked using this way.
External reference:
https://nodesecurity.io/advisories/67