diff --git a/config/v12/typo3-120.php b/config/v12/typo3-120.php
index 432878ad8..134e55b61 100644
--- a/config/v12/typo3-120.php
+++ b/config/v12/typo3-120.php
@@ -3,6 +3,9 @@
 declare(strict_types=1);
 
 use Rector\Config\RectorConfig;
+use Rector\Renaming\Rector\ClassConstFetch\RenameClassConstFetchRector;
+use Rector\Renaming\ValueObject\RenameClassAndConstFetch;
+use Rector\Renaming\ValueObject\RenameClassConstFetch;
 use Ssch\TYPO3Rector\FileProcessor\Resources\Files\Rector\v12\v0\RenameExtTypoScriptFilesFileRector;
 use Ssch\TYPO3Rector\Rector\Migrations\RenameClassMapAliasRector;
 use Ssch\TYPO3Rector\Rector\v12\v0\ReplacePreviewUrlMethodRector;
@@ -20,13 +23,14 @@
 use Ssch\TYPO3Rector\Rector\v12\v0\typo3\ReplaceTSFEWithContextMethodsRector;
 use Ssch\TYPO3Rector\Rector\v12\v0\typo3\SubstituteCompositeExpressionAddMethodsRector;
 use Ssch\TYPO3Rector\Rector\v12\v0\typo3\UseCompositeExpressionStaticMethodsRector;
+use TYPO3\CMS\Core\Messaging\AbstractMessage;
 
 return static function (RectorConfig $rectorConfig): void {
-    $rectorConfig->import(__DIR__ . '/../config.php');
+    $rectorConfig->import(__DIR__.'/../config.php');
     $rectorConfig->rule(RenameExtTypoScriptFilesFileRector::class);
     $rectorConfig->ruleWithConfiguration(RenameClassMapAliasRector::class, [
-        __DIR__ . '/../../Migrations/TYPO3/12.0/typo3/sysext/backend/Migrations/Code/ClassAliasMap.php',
-        __DIR__ . '/../../Migrations/TYPO3/12.0/typo3/sysext/frontend/Migrations/Code/ClassAliasMap.php',
+        __DIR__.'/../../Migrations/TYPO3/12.0/typo3/sysext/backend/Migrations/Code/ClassAliasMap.php',
+        __DIR__.'/../../Migrations/TYPO3/12.0/typo3/sysext/frontend/Migrations/Code/ClassAliasMap.php',
     ]);
     $rectorConfig->rule(ReplacePreviewUrlMethodRector::class);
     $rectorConfig->rule(AddMethodToWidgetInterfaceClassesRector::class);
@@ -43,4 +47,101 @@
     $rectorConfig->rule(ReplaceTSFEWithContextMethodsRector::class);
     $rectorConfig->rule(SubstituteCompositeExpressionAddMethodsRector::class);
     $rectorConfig->rule(UseCompositeExpressionStaticMethodsRector::class);
+
+    # https://docs.typo3.org/c/typo3/cms-core/master/en-us/Changelog/12.0/Deprecation-97787-SeveritiesOfFlashMessagesAndReportsDeprecated.html
+    $rectorConfig->ruleWithConfiguration(
+        RenameClassConstFetchRector::class,
+        [
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\AbstractMessage',
+                'NOTICE',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'NOTICE'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\AbstractMessage',
+                'INFO',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'INFO'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\AbstractMessage',
+                'OK',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'OK'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\AbstractMessage',
+                'WARNING',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'WARNING'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\AbstractMessage',
+                'ERROR',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'ERROR'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\FlashMessage',
+                'NOTICE',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'NOTICE'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\FlashMessage',
+                'INFO',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'INFO'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\FlashMessage',
+                'OK',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'OK'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\FlashMessage',
+                'WARNING',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'WARNING'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Core\Messaging\FlashMessage',
+                'ERROR',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'ERROR'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Reports\Status',
+                'NOTICE',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'NOTICE'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Reports\Status',
+                'INFO',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'INFO'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Reports\Status',
+                'OK',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'OK'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Reports\Status',
+                'WARNING',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'WARNING'
+            ),
+            new RenameClassAndConstFetch(
+                'TYPO3\CMS\Reports\Status',
+                'ERROR',
+                'TYPO3\CMS\Core\Type\ContextualFeedbackSeverity',
+                'ERROR'
+            ),
+        ]
+    );
 };
diff --git a/stubs/TYPO3/CMS/Core/Messaging/AbstractMessage.php b/stubs/TYPO3/CMS/Core/Messaging/AbstractMessage.php
new file mode 100644
index 000000000..dc7271393
--- /dev/null
+++ b/stubs/TYPO3/CMS/Core/Messaging/AbstractMessage.php
@@ -0,0 +1,22 @@
+<?php
+namespace TYPO3\CMS\Core\Messaging;
+
+use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;
+
+if (class_exists('TYPO3\CMS\Core\Messaging\AbstractMessage')) {
+    return;
+}
+
+abstract class AbstractMessage implements \JsonSerializable
+{
+    const NOTICE = -2;
+    const INFO = -1;
+    const OK = 0;
+    const WARNING = 1;
+    const ERROR = 2;
+
+    public function setSeverity($severity = ContextualFeedbackSeverity::OK): void
+    {
+
+    }
+}
diff --git a/stubs/TYPO3/CMS/Core/Messaging/FlashMessage.php b/stubs/TYPO3/CMS/Core/Messaging/FlashMessage.php
new file mode 100644
index 000000000..ead9d1df3
--- /dev/null
+++ b/stubs/TYPO3/CMS/Core/Messaging/FlashMessage.php
@@ -0,0 +1,14 @@
+<?php
+namespace TYPO3\CMS\Core\Messaging;
+
+if (class_exists('TYPO3\CMS\Core\Messaging\FlashMessage')) {
+    return;
+}
+
+class FlashMessage extends AbstractMessage
+{
+    public function jsonSerialize()
+    {
+        return [];
+    }
+}
diff --git a/stubs/TYPO3/CMS/Core/Type/ContextualFeedbackSeverity.php b/stubs/TYPO3/CMS/Core/Type/ContextualFeedbackSeverity.php
new file mode 100644
index 000000000..ccc41d166
--- /dev/null
+++ b/stubs/TYPO3/CMS/Core/Type/ContextualFeedbackSeverity.php
@@ -0,0 +1,15 @@
+<?php
+namespace TYPO3\CMS\Core\Type;
+
+if (class_exists('TYPO3\CMS\Core\Type\ContextualFeedbackSeverity')) {
+    return;
+}
+
+class ContextualFeedbackSeverity
+{
+    const NOTICE = -2;
+    const INFO = -1;
+    const OK = 0;
+    const WARNING = 1;
+    const ERROR = 2;
+}
diff --git a/stubs/TYPO3/CMS/Reports/Status.php b/stubs/TYPO3/CMS/Reports/Status.php
new file mode 100644
index 000000000..f28429ff3
--- /dev/null
+++ b/stubs/TYPO3/CMS/Reports/Status.php
@@ -0,0 +1,29 @@
+<?php
+namespace TYPO3\CMS\Reports;
+
+use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;
+
+if (class_exists('TYPO3\CMS\Reports\Status')) {
+    return;
+}
+
+class Status
+{
+    const NOTICE = -2;
+    const INFO = -1;
+    const OK = 0;
+    const WARNING = 1;
+    const ERROR = 2;
+
+    private int $severity;
+
+    public function __construct($severity = ContextualFeedbackSeverity::OK)
+    {
+        $this->severity = $severity;
+    }
+
+    public function getSeverity(): int
+    {
+        return $this->severity;
+    }
+}
diff --git a/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/Fixture/fixture.php.inc b/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/Fixture/fixture.php.inc
new file mode 100644
index 000000000..5d9770b48
--- /dev/null
+++ b/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/Fixture/fixture.php.inc
@@ -0,0 +1,44 @@
+<?php
+
+namespace Ssch\TYPO3Rector\Tests\Rector\v12\v0\typo3\ReplaceSeveritiesFlashMessageAndReportsRector\Fixture;
+
+use TYPO3\CMS\Core\Messaging\FlashMessage;
+use TYPO3\CMS\Reports\Status;
+
+$flashMessage = new FlashMessage();
+$flashMessage->setSeverity(FlashMessage::NOTICE);
+$flashMessage->setSeverity(FlashMessage::ERROR);
+$flashMessage->setSeverity(FlashMessage::INFO);
+$flashMessage->setSeverity(FlashMessage::OK);
+$flashMessage->setSeverity(FlashMessage::WARNING);
+
+$statusNotice = new Status(Status::NOTICE);
+$statusInfo = new Status(Status::INFO);
+$statusWarning = new Status(Status::WARNING);
+$statusOk = new Status(Status::OK);
+$statusError = new Status(Status::ERROR);
+
+?>
+-----
+<?php
+
+namespace Ssch\TYPO3Rector\Tests\Rector\v12\v0\typo3\ReplaceSeveritiesFlashMessageAndReportsRector\Fixture;
+
+use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;
+use TYPO3\CMS\Core\Messaging\FlashMessage;
+use TYPO3\CMS\Reports\Status;
+
+$flashMessage = new FlashMessage();
+$flashMessage->setSeverity(ContextualFeedbackSeverity::NOTICE);
+$flashMessage->setSeverity(ContextualFeedbackSeverity::ERROR);
+$flashMessage->setSeverity(ContextualFeedbackSeverity::INFO);
+$flashMessage->setSeverity(ContextualFeedbackSeverity::OK);
+$flashMessage->setSeverity(ContextualFeedbackSeverity::WARNING);
+
+$statusNotice = new Status(ContextualFeedbackSeverity::NOTICE);
+$statusInfo = new Status(ContextualFeedbackSeverity::INFO);
+$statusWarning = new Status(ContextualFeedbackSeverity::WARNING);
+$statusOk = new Status(ContextualFeedbackSeverity::OK);
+$statusError = new Status(ContextualFeedbackSeverity::ERROR);
+
+?>
diff --git a/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/ReplaceSeveritiesFlashMessageAndReportsRector.php b/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/ReplaceSeveritiesFlashMessageAndReportsRector.php
new file mode 100644
index 000000000..fbd960af9
--- /dev/null
+++ b/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/ReplaceSeveritiesFlashMessageAndReportsRector.php
@@ -0,0 +1,34 @@
+<?php
+declare(strict_types=1);
+
+
+namespace Ssch\TYPO3Rector\Tests\Rector\v12\v0\typo3\ReplaceSeveritiesFlashMessageAndReportsRector;
+
+
+use Iterator;
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+use Symplify\SmartFileSystem\SmartFileInfo;
+
+final class ReplaceSeveritiesFlashMessageAndReportsRector extends AbstractRectorTestCase
+{
+    /**
+     * @dataProvider provideData()
+     */
+    public function test(SmartFileInfo $fileInfo): void
+    {
+        $this->doTestFileInfo($fileInfo);
+    }
+
+    /**
+     * @return Iterator<SmartFileInfo>
+     */
+    public function provideData(): Iterator
+    {
+        return $this->yieldFilesFromDirectory(__DIR__ . '/Fixture');
+    }
+
+    public function provideConfigFilePath(): string
+    {
+        return __DIR__ . '/config/configured_rule.php';
+    }
+}
diff --git a/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/config/configured_rule.php b/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/config/configured_rule.php
new file mode 100644
index 000000000..7a928a706
--- /dev/null
+++ b/tests/Rector/v12/v0/typo3/ReplaceSeveritiesFlashMessageAndReportsRector/config/configured_rule.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+
+use Ssch\TYPO3Rector\Rector\v12\v0\typo3\ReplaceExpressionBuilderMethodsRector;
+
+return static function (RectorConfig $rectorConfig): void {
+    $rectorConfig->import(__DIR__ . '/../../../../../../../config/config_test.php');
+    $rectorConfig->import(__DIR__ . '/../../../../../../../config/v12/typo3-120.php');
+};