R5 A6 Sensitive Data Exposure Model Attributes Exposure

Description

The application's API returns a model object (user or users). Using respond_with, the API returns the full model object. It is simple but exposes information such as the user's password and other user attributes that you may wish to keep invisible.

Bug

Within app/controllers/api/v1/users_controller.rb:

def index
  # We removed the .as_json code from the model, just seemed like extra work.
  # dunno, maybe useful at a later time?
  #respond_with @user.admin ? User.all.as_json : @user.as_json
  
  respond_with @user.admin ? User.all : @user
end

def show
  respond_with @user.as_json
end

The as_json method referenced in the comments section of the index action exists within the user model in order to override and safely protect our model from only rendering certain attributes. It is unused (commented out), app/models/user.rb:

# Instead of the entire user object being returned, we can use this to filter.
def as_json
  super(only: [:id, :email, :first_name, :last_name])
end

The as_json method referenced in the comments section of the index action exists within the user model in order to override and safely protect our model from only rendering certain attributes. It is unused (commented out), app/models/user.rb:

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
X-UA-Compatible: IE=Edge
ETag: "6b4caf343a20865de174b2b530b945dd"
Cache-Control: max-age=0, private, must-revalidate
X-Request-Id: c3b0a57861087c0b827aab231747ef0c
X-Runtime: 0.051734
Connection: close

{"admin":false,"created_at":"2014-01-23T16:17:10Z","email":
"mike@metacorp.com","first_name":"Mike","id":5,"last_name":"McCabe","password":
"b46dd2888a0904972649cc880a93f4dd","updated_at":"2014-01-23T16:17:10Z","id":5}

Note that all attributes associated with this user are returned via the API.

Solution

Model Attributes Exposure - ATTACK

Use the API and review the data returned. Additional information on exploiting the API available here.

Model Attributes Exposure - SOLUTION

Uncomment the as_json method within the user model. Additionally, call .as_json on any User model object you would like to return via the API or other means. Example:

respond_with @user.admin ? User.all.as_json : @user.as_json

Upon uncommenting the as_json method within the User model, the as_json method will ensure the API output only returns those attributes you have allowed in the following code:

def as_json
  super(only: [:id, :email, :first_name, :last_name])
end

The response from the API should look like:

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
X-UA-Compatible: IE=Edge
ETag: "2333488e856669ac637e37cb4cf09cb6"
Cache-Control: max-age=0, private, must-revalidate
X-Request-Id: baa6a1c90004838793614e4c61633767
X-Runtime: 0.092768
Connection: close

{"email":"mike@metacorp.com","first_name":"Mike","last_name":"McCabe","id":5}

Hint

We have an API available... what does it return?