Schema does not define the type of JSON values

Description

The API defines a schema for a JSON payload. However, the schema does not define the types of the values in it.

For more details, see the OpenAPI Specification.

Example

The following is an example of how this type of risk could look in your API definition. The object NewPet is defined in #/definitions and referenced as the schema for the API method. However, the types of the properties in the object (name and tag) are not defined:

"post": {
  "description": "Creates a new pet in the store",
  "operationId": "addPet",
  "parameters": [
    {
      "name": "pet",
      "in": "body",
      "description": "pet to add to the system",
      "required": true,
      "schema": {
        "$ref": "#/definitions/NewPet"
      }
    }
  ]
}
...
{
  "NewPet": {
    "type": "object",
    "required": [
      "name"
    ],
    "properties": {
      "name": {
        "description": "Pet name"
      },
      "tag": {
        "description": "Pet tag"
      }
    }
  }
}

Possible exploit scenario

If do not clearly define the schema and properties of a JSON payload empty, you effectively allow attackers to pass in any data. This means that you are opening your backend to various attacks, such as SQL injection.

This also lets attackers to try various unexpected inputs. Unexpected inputs may cause the backend server to crash or behave in an unexpected way. This in turn may cause the server to potentially leak stack trace that can be used for further attacks, or even data.

Remediation

Make sure you define all properties of the accepted JSON payloads.

"post": {
  "description": "Creates a new pet in the store",
  "operationId": "addPet",
  "parameters": [
    {
      "name": "pet",
      "in": "body",
      "description": "pet to add to the system",
      "required": true,
      "schema": {
        "$ref": "#/definitions/NewPet"
      }
    }
  ]
}
...
{
  "NewPet": {
    "type": "object",
    "required": [
      "name"
    ],
    "properties": {
      "name": {
        "type": "string"
      },
      "tag": {
        "type": "string"
      }
    }
  }
}