Protect against CSV Injection

lib/active_admin/csv_builder.rb

@@ -51,7 +51,7 @@ def build(controller, csv)
       csv << bom if bom
 
       if column_names
-        csv << CSV.generate_line(columns.map { |c| encode c.name, options }, **csv_options)
+        csv << CSV.generate_line(columns.map { |c| sanitize(encode(c.name, options)) }, **csv_options)
       end
 
       controller.send(:in_paginated_batches) do |resource|
@@ -70,7 +70,7 @@ def exec_columns(view_context = nil)
 
     def build_row(resource, columns, options)
       columns.map do |column|
-        encode call_method_or_proc_on(resource, column.data), options
+        sanitize(encode(call_method_or_proc_on(resource, column.data), options))
       end
     end
 
@@ -86,6 +86,10 @@ def encode(content, options)
       end
     end
 
+    def sanitize(content)
+      Sanitizer.sanitize(content)
+    end
+
     def method_missing(method, *args, &block)
       if @view_context.respond_to? method
         @view_context.public_send method, *args, &block
@@ -120,4 +124,21 @@ def column_transitive_options
       @column_transitive_options ||= @options.slice(*COLUMN_TRANSITIVE_OPTIONS)
     end
   end
+
+  # Prevents CSV Injection according to https://owasp.org/www-community/attacks/CSV_Injection
+  module Sanitizer
+    extend self
+
+    ATTACK_CHARACTERS = ['=', '+', '-', '@', "\t", "\r"].freeze
+
+    def sanitize(value)
+      return "'#{value}" if require_sanitization?(value)
+
+      value
+    end
+
+    def require_sanitization?(value)
+      value.is_a?(String) && value.starts_with?(*ATTACK_CHARACTERS)
+    end
+  end
 end

spec/unit/csv_builder_spec.rb

@@ -277,4 +277,52 @@ def view_context
       end
     end
   end
+
+  context 'csv injection' do
+    let(:dummy_controller) do
+      class DummyController
+        def in_paginated_batches(&block)
+          Post.all.each(&block)
+        end
+
+        def view_context
+          MethodOrProcHelper
+        end
+      end
+      DummyController.new
+    end
+
+    let(:builder) do
+      ActiveAdmin::CSVBuilder.new do
+        column(:id)
+        column(:title)
+      end
+    end
+
+    ['=', '+', '-', '@', "\t", "\r"].each do |char|
+      it "prepends a single quote when column starts with a #{char} character" do
+        attack = "#{char}1+2"
+
+        escaped_attack = "'#{attack}"
+        escaped_attack = "\"#{escaped_attack}\"" if char == "\r"
+
+        post = Post.create!(title: attack)
+        receiver = []
+        builder.build dummy_controller, receiver
+        line = receiver.last
+        expect(line).to eq "#{post.id},#{escaped_attack}\n"
+      end
+
+      it "accounts for the field separator when character #{char} is used to inject a formula" do
+        attack = "#{char}1+2'\" ;,#{char}1+2"
+        escaped_attack = "\"'#{attack.gsub('"', '""')}\""
+
+        post = Post.create!(title: attack)
+        receiver = []
+        builder.build dummy_controller, receiver
+        line = receiver.last
+        expect(line).to eq "#{post.id},#{escaped_attack}\n"
+      end
+    end
+  end
 end