diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index ae2851ed221..5e8e22a6042 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -19,6 +19,7 @@ use Drupal\Core\Security\TrustedCallbackInterface;
 use Drupal\Core\Theme\ThemeManagerInterface;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\HttpFoundation\FileBag;
+use Symfony\Component\HttpFoundation\ParameterBag;
 use Symfony\Component\HttpFoundation\RequestStack;
 use Symfony\Component\HttpFoundation\Response;
 
@@ -957,8 +958,16 @@ class FormBuilder implements FormBuilderInterface, FormValidatorInterface, FormS
             // This value is checked in self::handleInputElement().
             $form_state->setInvalidToken(TRUE);
 
+            // Ignore all submitted values.
+            $form_state->setUserInput([]);
+
+            $request = $this->requestStack->getCurrentRequest();
+            // Do not trust any POST data.
+            $request->request = new ParameterBag();
             // Make sure file uploads do not get processed.
-            $this->requestStack->getCurrentRequest()->files = new FileBag();
+            $request->files = new FileBag();
+            // Ensure PHP globals reflect these changes.
+            $request->overrideGlobals();
           }
         }
       }
diff --git a/core/lib/Drupal/Core/Form/FormValidator.php b/core/lib/Drupal/Core/Form/FormValidator.php
index 57d24cc21e7..2afcb52ba9d 100644
--- a/core/lib/Drupal/Core/Form/FormValidator.php
+++ b/core/lib/Drupal/Core/Form/FormValidator.php
@@ -124,10 +124,8 @@ class FormValidator implements FormValidatorInterface {
    * {@inheritdoc}
    */
   public function setInvalidTokenError(FormStateInterface $form_state) {
-    $url = $this->requestStack->getCurrentRequest()->getRequestUri();
-
     // Setting this error will cause the form to fail validation.
-    $form_state->setErrorByName('form_token', $this->t('The form has become outdated. Copy any unsaved work in the form below and then <a href=":link">reload this page</a>.', [':link' => $url]));
+    $form_state->setErrorByName('form_token', $this->t('The form has become outdated. Press the back button, copy any unsaved work in the form, and then reload the page.'));
   }
 
   /**
diff --git a/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php b/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php
index 348cee7d3a9..3f67a7948a8 100644
--- a/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php
+++ b/core/modules/file/tests/src/Functional/FileManagedFileElementTest.php
@@ -50,7 +50,7 @@ class FileManagedFileElementTest extends FileFieldTestBase {
             $file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri()),
           ];
           $this->drupalPostForm(NULL, $edit, t('Save'));
-          $this->assertText('The form has become outdated. Copy any unsaved work in the form below');
+          $this->assertText('The form has become outdated.');
           $last_fid = $this->getLastFileId();
           $this->assertEqual($last_fid_prior, $last_fid, 'File was not saved when uploaded with an invalid form token.');
 
diff --git a/core/modules/system/tests/src/Functional/Form/FormTest.php b/core/modules/system/tests/src/Functional/Form/FormTest.php
index bf5fb276464..39e304eee2f 100644
--- a/core/modules/system/tests/src/Functional/Form/FormTest.php
+++ b/core/modules/system/tests/src/Functional/Form/FormTest.php
@@ -251,21 +251,27 @@ class FormTest extends BrowserTestBase {
     $this->assertSession()
       ->elementExists('css', 'input[name="form_token"]')
       ->setValue('invalid token');
+    $random_string = $this->randomString();
     $edit = [
-      'textfield' => $this->randomString(),
+      'textfield' => $random_string,
       'checkboxes[bar]' => TRUE,
       'select' => 'bar',
       'radios' => 'foo',
     ];
     $this->drupalPostForm(NULL, $edit, 'Submit');
     $this->assertFieldByXpath('//div[contains(@class, "error")]', NULL, 'Error message is displayed with invalid token even when required fields are filled.');
-    $this->assertText('The form has become outdated. Copy any unsaved work in the form below');
-    // Verify that input elements retained the posted values.
-    $this->assertFieldByName('textfield', $edit['textfield']);
+
+    $assert = $this->assertSession();
+    $element = $assert->fieldExists('textfield');
+    $this->assertEmpty($element->getValue());
+    $assert->responseNotContains($random_string);
+    $this->assertText('The form has become outdated.');
+    // Ensure that we don't use the posted values.
+    $this->assertFieldByName('textfield', '');
     $this->assertNoFieldChecked('edit-checkboxes-foo');
-    $this->assertFieldChecked('edit-checkboxes-bar');
-    $this->assertOptionSelected('edit-select', 'bar');
-    $this->assertFieldChecked('edit-radios-foo');
+    $this->assertNoFieldChecked('edit-checkboxes-bar');
+    $this->assertOptionSelected('edit-select', '');
+    $this->assertNoFieldChecked('edit-radios-foo');
 
     // Check another form that has a textarea input.
     $this->drupalGet(Url::fromRoute('form_test.required'));
@@ -278,9 +284,9 @@ class FormTest extends BrowserTestBase {
     ];
     $this->drupalPostForm(NULL, $edit, 'Submit');
     $this->assertFieldByXpath('//div[contains(@class, "error")]', NULL, 'Error message is displayed with invalid token even when required fields are filled.');
-    $this->assertText('The form has become outdated. Copy any unsaved work in the form below');
-    $this->assertFieldByName('textfield', $edit['textfield']);
-    $this->assertFieldByName('textarea', $edit['textarea']);
+    $this->assertText('The form has become outdated.');
+    $this->assertFieldByName('textfield', '');
+    $this->assertFieldByName('textarea', '');
 
     // Check another form that has a number input.
     $this->drupalGet(Url::fromRoute('form_test.number'));
@@ -288,12 +294,14 @@ class FormTest extends BrowserTestBase {
       ->elementExists('css', 'input[name="form_token"]')
       ->setValue('invalid token');
     $edit = [
-      'integer_step' => mt_rand(1, 100),
+      // We choose a random value which is higher than the default value,
+      // so we don't accidentally generate the default value.
+      'integer_step' => mt_rand(6, 100),
     ];
     $this->drupalPostForm(NULL, $edit, 'Submit');
     $this->assertFieldByXpath('//div[contains(@class, "error")]', NULL, 'Error message is displayed with invalid token even when required fields are filled.');
-    $this->assertText('The form has become outdated. Copy any unsaved work in the form below');
-    $this->assertFieldByName('integer_step', $edit['integer_step']);
+    $this->assertText('The form has become outdated.');
+    $this->assertFieldByName('integer_step', 5);
 
     // Check a form with a Url field
     $this->drupalGet(Url::fromRoute('form_test.url'));
@@ -305,8 +313,8 @@ class FormTest extends BrowserTestBase {
     ];
     $this->drupalPostForm(NULL, $edit, 'Submit');
     $this->assertFieldByXpath('//div[contains(@class, "error")]', NULL, 'Error message is displayed with invalid token even when required fields are filled.');
-    $this->assertText('The form has become outdated. Copy any unsaved work in the form below');
-    $this->assertFieldByName('url', $edit['url']);
+    $this->assertText('The form has become outdated.');
+    $this->assertFieldByName('url', '');
   }
 
   /**
diff --git a/core/modules/system/tests/src/Functional/Form/ValidationTest.php b/core/modules/system/tests/src/Functional/Form/ValidationTest.php
index 3ae3ffee1ac..9834eef8bb6 100644
--- a/core/modules/system/tests/src/Functional/Form/ValidationTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ValidationTest.php
@@ -74,7 +74,7 @@ class ValidationTest extends BrowserTestBase {
     $this->drupalPostForm(NULL, ['name' => 'validate'], 'Save');
     $this->assertNoFieldByName('name', '#value changed by #validate', 'Form element #value was not altered.');
     $this->assertNoText('Name value: value changed by setValueForElement() in #validate', 'Form element value in $form_state was not altered.');
-    $this->assertText('The form has become outdated. Copy any unsaved work in the form below');
+    $this->assertText('The form has become outdated.');
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php b/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
index 2b3de5de53d..8060341d32e 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormBuilderTest.php
@@ -832,12 +832,30 @@ class FormBuilderTest extends FormTestBase {
     $expected_form = $form_id();
     $form_arg = $this->getMockForm($form_id, $expected_form);
 
+    // Set up some request data so we can be sure it is removed when a token is
+    // invalid.
+    $this->request->request->set('foo', 'bar');
+    $_POST['foo'] = 'bar';
+
     $form_state = new FormState();
     $input['form_id'] = $form_id;
     $input['form_token'] = $form_token;
+    $input['test'] = 'example-value';
     $form_state->setUserInput($input);
-    $this->simulateFormSubmission($form_id, $form_arg, $form_state, FALSE);
+    $form = $this->simulateFormSubmission($form_id, $form_arg, $form_state, FALSE);
     $this->assertSame($expected, $form_state->hasInvalidToken());
+    if ($expected) {
+      $this->assertEmpty($form['test']['#value']);
+      $this->assertEmpty($form_state->getValue('test'));
+      $this->assertEmpty($_POST);
+      $this->assertEmpty(iterator_to_array($this->request->request->getIterator()));
+    }
+    else {
+      $this->assertEquals('example-value', $form['test']['#value']);
+      $this->assertEquals('example-value', $form_state->getValue('test'));
+      $this->assertEquals('bar', $_POST['foo']);
+      $this->assertEquals('bar', $this->request->request->get('foo'));
+    }
   }
 
   public function providerTestInvalidToken() {
diff --git a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
index 5e4b64c4dd8..56264ece281 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
@@ -173,7 +173,7 @@ abstract class FormTestBase extends UnitTestCase {
       ->getMock();
     $this->account = $this->createMock('Drupal\Core\Session\AccountInterface');
     $this->themeManager = $this->createMock('Drupal\Core\Theme\ThemeManagerInterface');
-    $this->request = new Request();
+    $this->request = Request::createFromGlobals();
     $this->eventDispatcher = $this->createMock('Symfony\Component\EventDispatcher\EventDispatcherInterface');
     $this->requestStack = new RequestStack();
     $this->requestStack->push($this->request);
diff --git a/core/tests/Drupal/Tests/Core/Form/FormValidatorTest.php b/core/tests/Drupal/Tests/Core/Form/FormValidatorTest.php
index 9b1b73ef338..7eb5524a690 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormValidatorTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormValidatorTest.php
@@ -131,7 +131,7 @@ class FormValidatorTest extends UnitTestCase {
       ->getMock();
     $form_state->expects($this->once())
       ->method('setErrorByName')
-      ->with('form_token', 'The form has become outdated. Copy any unsaved work in the form below and then <a href="/test/example?foo=bar">reload this page</a>.');
+      ->with('form_token', 'The form has become outdated. Press the back button, copy any unsaved work in the form, and then reload the page.');
     $form_state->setValue('form_token', 'some_random_token');
     $form_validator->validateForm('test_form_id', $form, $form_state);
     $this->assertTrue($form_state->isValidationComplete());