diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 8633a264f..46e1e0415 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -579,13 +579,6 @@ Security/Eval:
     - 'app/models/user.rb'
     - 'config/initializers/00-core_plugins.rb'
 
-# This cop supports unsafe autocorrection (--autocorrect-all).
-Security/IoMethods:
-  Exclude:
-    - 'app/models/attachment.rb'
-    - 'test/functional/mail_handler_controller_test.rb'
-    - 'test/unit/mail_handler_test.rb'
-
 # This cop supports safe autocorrection (--autocorrect).
 # Configuration parameters: EnforcedStyle.
 # SupportedStyles: separated, grouped
diff --git a/app/models/attachment.rb b/app/models/attachment.rb
index 6ac97daf3..2dd43f6b8 100644
--- a/app/models/attachment.rb
+++ b/app/models/attachment.rb
@@ -454,7 +454,7 @@ class Attachment < ApplicationRecord
           filename = "#{basename}(#{dup_count})#{extname}"
         end
         zos.put_next_entry(filename)
-        zos << IO.binread(attachment.diskfile)
+        zos << File.binread(attachment.diskfile)
         archived_file_names << filename
       end
     end
diff --git a/test/functional/mail_handler_controller_test.rb b/test/functional/mail_handler_controller_test.rb
index b27f3dc8a..10ac3831e 100644
--- a/test/functional/mail_handler_controller_test.rb
+++ b/test/functional/mail_handler_controller_test.rb
@@ -38,7 +38,7 @@ class MailHandlerControllerTest < Redmine::ControllerTest
           :params => {
             :key => 'secret',
             :email =>
-               IO.read(
+               File.read(
                  File.join(FIXTURES_PATH, 'ticket_on_given_project.eml')
                )
           }
@@ -60,7 +60,7 @@ class MailHandlerControllerTest < Redmine::ControllerTest
           :params => {
             :key => 'secret',
             :email =>
-              IO.read(
+              File.read(
                 File.join(FIXTURES_PATH, 'ticket_on_given_project.eml')
               ),
             :issue => {
@@ -87,7 +87,7 @@ class MailHandlerControllerTest < Redmine::ControllerTest
             :index,
             :params => {
               :key => 'secret',
-              :email => IO.read(File.join(FIXTURES_PATH, 'ticket_reply.eml'))
+              :email => File.read(File.join(FIXTURES_PATH, 'ticket_reply.eml'))
             }
           )
         end
@@ -108,7 +108,7 @@ class MailHandlerControllerTest < Redmine::ControllerTest
           :params => {
             :key => 'secret',
             :email =>
-              IO.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
+              File.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
           }
         )
       end
@@ -128,7 +128,7 @@ class MailHandlerControllerTest < Redmine::ControllerTest
           :params => {
             :key => 'secret',
             :email =>
-              IO.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
+              File.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
           }
         )
       end
@@ -148,7 +148,7 @@ class MailHandlerControllerTest < Redmine::ControllerTest
           :params => {
             :key => 'wrong',
             :email =>
-              IO.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
+              File.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
           }
         )
       end
diff --git a/test/unit/mail_handler_test.rb b/test/unit/mail_handler_test.rb
index 1d1a02a35..94ef541e7 100644
--- a/test/unit/mail_handler_test.rb
+++ b/test/unit/mail_handler_test.rb
@@ -907,7 +907,7 @@ class MailHandlerTest < ActiveSupport::TestCase
       "Auto-Submitted: auto-generated",
       'X-Autoreply: yes'
     ].each do |header|
-      raw = IO.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
+      raw = File.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
       raw = header + "\n" + raw
 
       assert_no_difference 'Issue.count' do
@@ -920,7 +920,7 @@ class MailHandlerTest < ActiveSupport::TestCase
     [
       "Auto-Submitted: auto-forwarded"
     ].each do |header|
-      raw = IO.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
+      raw = File.read(File.join(FIXTURES_PATH, 'ticket_on_given_project.eml'))
       raw = header + "\n" + raw
 
       assert_difference 'Issue.count', 1 do
@@ -1493,7 +1493,7 @@ class MailHandlerTest < ActiveSupport::TestCase
   private
 
   def submit_email(filename, options={})
-    raw = IO.read(File.join(FIXTURES_PATH, filename))
+    raw = File.read(File.join(FIXTURES_PATH, filename))
     yield raw if block_given?
     MailHandler.receive(raw, options)
   end