Prevention of user enumeration
class UsersController < ApplicationController
def show
@user = User.find(params[:id])
if @user
render json: { user: @user }
else
render json: { error: 'User not found' }, status: :not_found
end
end
end
The above code is a
show
action in a
UsersController
in a Ruby on Rails application. This action is used to fetch a user's details based on the user ID passed in the request parameters.
The vulnerability lies in the way the application handles non-existent users. If a user exists, the application returns the user's details in the response. If the user does not exist, the application returns a different response
- an error message stating 'User not found' and a status of
:not_found
.
This difference in responses can be exploited by an attacker to enumerate valid users. By sending a series of requests with different user IDs, an attacker can distinguish between existent and non-existent users based on the response they receive. For example, if they receive a user's details, they know the user ID is valid. If they receive the 'User not found' error, they know the user ID is not valid.
This is a User Enumeration vulnerability because it allows an attacker to identify valid users in the system. This information can be used for further attacks, such as password guessing attacks, targeted phishing attacks, and more.
class UsersController < ApplicationController
def show
@user = User.find_by(id: params[:id])
if @user
render json: { user: @user }
else
render json: { error: 'An error occurred' }, status: :not_found
end
end
end
The updated code implements a consistent error response for both existent and non-existent users. This is achieved by using the
find_by
method instead of
find
. The
find_by
method returns
nil
if no record is found, unlike
find
which raises an exception. This allows us to handle both cases in the same way and return a consistent error message.
The error message has been changed from 'User not found' to 'An error occurred'. This is a more generic message that does not disclose whether a user exists or not, preventing user enumeration.
Please note that this code fix is just one part of the solution. To fully protect against user enumeration, you should also consider implementing additional measures such as response time padding, rate limiting, CAPTCHA, and regular log analysis, as mentioned in the steps to fix the vulnerability.