Class: Scryer::Rules::MassAssignmentRule

Inherits:
Scryer::Rule show all
Defined in:
lib/scryer/rules/mass_assignment_rule.rb

Overview

Flags Model.new(params[...]) / Model.new(params) / .update(params[...]) / .assign_attributes(params) where the argument is params (or a subscript of it) with no .permit(...) anywhere in the same argument expression — i.e. attributes are being mass-assigned straight from the request with no allow-list.

Constant Summary collapse

ASSIGNMENT_METHODS = 
%w[new create create! update update! assign_attributes attributes=].freeze
IVAR_RECEIVER_METHODS =

update/update!/assign_attributes/attributes= on an instance variable (@order.update(params[:order])) is at least as common a real-world shape as Model.new(...)/Model.create(...) on a bare constant — the standard before_action :set_thing + @thing.update scaffold pattern — but was invisible to this rule entirely until found via the accuracy benchmark (benchmark/corpus.rb's "mass_assignment" vulnerable sample), since likely_model_receiver? only accepted a bare constant or implicit (nil) receiver. .new/ create/create! deliberately stay constant/nil-only: those verbs only make sense as a receiver-less/class-level call in normal Rails code, whereas an ivar could just as easily be a plain Hash (Hash# update is a real merge! alias) — restricting the ivar allowance to only the update-style verbs keeps this from also matching things like @filters.update(params[:filters]) on a Hash.

%w[update update! assign_attributes attributes=].freeze
NON_MODEL_RECEIVERS =

Common stdlib/gem constants with their own .new/.create-style factory methods that have nothing to do with ActiveRecord mass assignment (e.g. BCrypt::Password.create(params[:password]) is hashing a single value, not setting a hash of model attributes). Excluding these — plus anything referenced through a namespaced A::B path, which real Rails models are less commonly called via at the exact call site — cuts down false positives significantly.

%w[
  Struct OpenStruct Data Class Module BCrypt OpenSSL Net URI Digest
  JSON YAML Marshal String Array Hash Integer Float Symbol Comparable
].freeze

Instance Attribute Summary

Attributes inherited from Scryer::Rule

#file, #sexp, #source

Instance Method Summary collapse

Methods inherited from Scryer::Rule

inherited, #initialize

Constructor Details

This class inherits a constructor from Scryer::Rule

Instance Method Details

#scan ⇒ Object 



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# File 'lib/scryer/rules/mass_assignment_rule.rb', line 47

def scan
  findings = []

  Ast.each_node(sexp) do |node|
    next unless Ast.tagged?(node, :method_add_arg, :command, :command_call)

    inner = Ast.tagged?(node, :method_add_arg) ? node[1] : node
    receiver_and_name = Ast.call_name(inner)
    next unless receiver_and_name

    receiver, method_name = receiver_and_name
    next unless ASSIGNMENT_METHODS.include?(method_name)
    next unless likely_model_receiver?(receiver, method_name)

    args = Ast.call_arguments(node)
    next if args.empty?

    arg = args.first
    next unless references_raw_params?(arg)

    line = Ast.line_of(arg) || Ast.line_of(node)
    findings << finding(
      line: line,
      message: "`#{method_name}` receives `params` (or a subscript of it) directly, " \
                "with no `.permit(...)` call — every attribute in the request can be " \
                "set, including ones the form/API was never meant to expose (e.g. `admin`, `role_id`).",
      suggested_fix: "Wrap the params in a strong-parameters method, e.g. " \
                      "`#{method_name}(order_params)` with `def order_params; " \
                      "params.require(:order).permit(:status, :total); end` — only the " \
                      "explicitly permitted keys get through."
    )
  end

  findings
end