Fix Mass Assignment in Roda

Mass Assignment in Roda typically manifests when raw request parameters are piped directly into Sequel model setters or constructors. An attacker can inject unauthorized fields—like 'is_admin' or 'role_id'—into the HTTP request to escalate privileges or bypass business logic. In a Roda context, the lack of a built-in 'Strong Parameters' layer means the burden of attribute whitelisting falls entirely on the developer's implementation of the routing tree.

The Vulnerable Pattern

# DANGER: Blindly passing the entire params hash to the model
r.post "update_profile" do
  @user = User[session[:user_id]]
  # Attacker sends user[admin]=true in POST body
  @user.update(r.params['user'])
  r.redirect "/dashboard"
end

The Secure Implementation

To kill Mass Assignment, you must implement strict attribute whitelisting. The vulnerable example uses Sequel's #update method, which accepts any key-value pair provided by the client. The fix utilizes #set_fields (or #update_fields), which requires an explicit array of allowed symbols. If an attacker attempts to inject 'admin' or 'password_hash', the ORM will ignore those keys because they aren't in the whitelist. Always treat 'r.params' as tainted input and never pass it unfiltered to your persistence layer.

# SECURE: Using Sequel's set_fields to whitelist attributes
r.post "update_profile" do
  @user = User[session[:user_id]]
  # Only 'bio' and 'location' can be modified via this request
  @user.set_fields(r.params['user'], [:bio, :location])
  @user.save
  r.redirect "/dashboard"
end