diff --git a/config/v9/typo3-90.php b/config/v9/typo3-90.php
index 4600db60f..4e50a7275 100644
--- a/config/v9/typo3-90.php
+++ b/config/v9/typo3-90.php
@@ -23,6 +23,7 @@
 use Ssch\TYPO3Rector\Rector\v9\v0\ReplaceAnnotationRector;
 use Ssch\TYPO3Rector\Rector\v9\v0\SubstituteCacheWrapperMethodsRector;
 use Ssch\TYPO3Rector\Rector\v9\v0\SubstituteConstantParsetimeStartRector;
+use Ssch\TYPO3Rector\Rector\v9\v0\UseExtensionConfigurationApiRector;
 use Ssch\TYPO3Rector\Rector\v9\v0\UseLogMethodInsteadOfNewLog2Rector;
 use Ssch\TYPO3Rector\Rector\v9\v0\UseNewComponentIdForPageTreeRector;
 use Ssch\TYPO3Rector\Rector\v9\v0\UseRenderingContextGetControllerContextRector;
@@ -94,4 +95,6 @@
     $services->set(UseNewComponentIdForPageTreeRector::class);
 
     $services->set(RefactorBackendUtilityGetPagesTSconfigRector::class);
+
+    $services->set(UseExtensionConfigurationApiRector::class);
 };
diff --git a/src/Helper/Typo3NodeResolver.php b/src/Helper/Typo3NodeResolver.php
index b90fc63ad..ce7ec7c05 100644
--- a/src/Helper/Typo3NodeResolver.php
+++ b/src/Helper/Typo3NodeResolver.php
@@ -53,7 +53,7 @@ final class Typo3NodeResolver
     /**
      * @var string
      */
-    private const GLOBALS = 'GLOBALS';
+    public const GLOBALS = 'GLOBALS';
 
     public function isMethodCallOnGlobals(Node $node, string $methodCall, string $global): bool
     {
diff --git a/src/Rector/v9/v0/UseExtensionConfigurationApiRector.php b/src/Rector/v9/v0/UseExtensionConfigurationApiRector.php
new file mode 100644
index 000000000..ce2176ac6
--- /dev/null
+++ b/src/Rector/v9/v0/UseExtensionConfigurationApiRector.php
@@ -0,0 +1,134 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ssch\TYPO3Rector\Rector\v9\v0;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\ArrayDimFetch;
+use PhpParser\Node\Expr\FuncCall;
+use Rector\Core\Rector\AbstractRector;
+use Rector\Core\RectorDefinition\CodeSample;
+use Rector\Core\RectorDefinition\RectorDefinition;
+use Ssch\TYPO3Rector\Helper\Typo3NodeResolver;
+use TYPO3\CMS\Core\Configuration\ExtensionConfiguration;
+use TYPO3\CMS\Core\Utility\GeneralUtility;
+
+/**
+ * @see https://docs.typo3.org/c/typo3/cms-core/master/en-us/Changelog/9.0/Deprecation-82254-DeprecateGLOBALSTYPO3_CONF_VARSEXTextConf.html
+ */
+final class UseExtensionConfigurationApiRector extends AbstractRector
+{
+    public function getNodeTypes(): array
+    {
+        return [FuncCall::class];
+    }
+
+    /**
+     * @param FuncCall $node
+     */
+    public function refactor(Node $node): ?Node
+    {
+        if (! $this->isName($node->name, 'unserialize')) {
+            return null;
+        }
+
+        $firstArgument = array_shift($node->args);
+
+        if (null === $firstArgument) {
+            return null;
+        }
+
+        if (! $firstArgument->value instanceof ArrayDimFetch) {
+            return null;
+        }
+
+        $extensionConfiguration = $firstArgument->value;
+
+        if ($this->shouldSkip($extensionConfiguration)) {
+            return null;
+        }
+
+        return $this->createMethodCall($this->createStaticCall(GeneralUtility::class, 'makeInstance', [
+            $this->createClassConstantReference(ExtensionConfiguration::class),
+        ]), 'get', [$extensionConfiguration->dim]);
+    }
+
+    /**
+     * @codeCoverageIgnore
+     */
+    public function getDefinition(): RectorDefinition
+    {
+        return new RectorDefinition(
+            'Use the new ExtensionConfiguration API instead of $GLOBALS[\'TYPO3_CONF_VARS\'][\'EXT\'][\'extConf\'][\'foo\']',
+            [
+                new CodeSample(<<<'PHP'
+$extensionConfiguration2 = unserialize($GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['foo'], ['allowed_classes' => false]);
+PHP
+                    , <<<'PHP'
+use TYPO3\CMS\Core\Configuration\ExtensionConfiguration;
+use TYPO3\CMS\Core\Utility\GeneralUtility;
+$extensionConfiguration2 = GeneralUtility::makeInstance(ExtensionConfiguration::class)->get('foo');
+PHP
+                ),
+
+            ]);
+    }
+
+    private function shouldSkip(ArrayDimFetch $node): bool
+    {
+        $extConf = $node->var;
+        if (! $extConf instanceof ArrayDimFetch) {
+            return true;
+        }
+
+        if (null === $extConf->dim) {
+            return true;
+        }
+
+        if (! $this->isValue($extConf->dim, 'extConf')) {
+            return true;
+        }
+
+        if (! property_exists($node->var, 'var')) {
+            return true;
+        }
+
+        $ext = $node->var->var;
+        if (! $ext instanceof ArrayDimFetch) {
+            return true;
+        }
+
+        if (null === $ext->dim) {
+            return true;
+        }
+
+        if (! $this->isValue($ext->dim, 'EXT')) {
+            return true;
+        }
+
+        $typo3ConfVars = $node->var->var->var;
+        if (! $typo3ConfVars instanceof ArrayDimFetch) {
+            return true;
+        }
+
+        if (null === $typo3ConfVars->dim) {
+            return true;
+        }
+
+        if (! $this->isValue($typo3ConfVars->dim, 'TYPO3_CONF_VARS')) {
+            return true;
+        }
+
+        $globals = $node->var->var->var->var;
+        if (! $this->isName($globals, Typo3NodeResolver::GLOBALS)) {
+            return true;
+        }
+
+        if (null === $node->dim) {
+            return true;
+        }
+
+        return ! $this->isName($node->dim, '_EXTKEY') && null === $this->getValue($node->dim);
+    }
+}
diff --git a/stubs/Core/Configuration/ExtensionConfiguration.php b/stubs/Core/Configuration/ExtensionConfiguration.php
new file mode 100644
index 000000000..3a093218f
--- /dev/null
+++ b/stubs/Core/Configuration/ExtensionConfiguration.php
@@ -0,0 +1,25 @@
+<?php
+declare(strict_types=1);
+
+namespace TYPO3\CMS\Core\Configuration;
+
+
+if (class_exists(ExtensionConfiguration::class)) {
+    return;
+}
+
+final class ExtensionConfiguration
+{
+    /**
+     * @return array
+     */
+    public function get(string $extension, string $path = '')
+    {
+        return [];
+    }
+
+    public function set(string $extension, string $path = '', $value = null): void
+    {
+    }
+
+}
diff --git a/stubs/Core/Utility/ExtensionManagementUtility.php b/stubs/Core/Utility/ExtensionManagementUtility.php
index 269162324..648a9416b 100644
--- a/stubs/Core/Utility/ExtensionManagementUtility.php
+++ b/stubs/Core/Utility/ExtensionManagementUtility.php
@@ -43,4 +43,8 @@ public static function configureModule($moduleSignature, $modulePath): array
     public static function loadExtLocalconf(bool $false): void
     {
     }
+
+    public static function extRelPath(string $key): void
+    {
+    }
 }
diff --git a/tests/Rector/v9/v0/UseExtensionConfigurationApi/Fixture/use_extension_configuration_api.php.inc b/tests/Rector/v9/v0/UseExtensionConfigurationApi/Fixture/use_extension_configuration_api.php.inc
new file mode 100644
index 000000000..02a5d95b3
--- /dev/null
+++ b/tests/Rector/v9/v0/UseExtensionConfigurationApi/Fixture/use_extension_configuration_api.php.inc
@@ -0,0 +1,23 @@
+<?php
+
+$extensionConfiguration2 = unserialize($GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['foo'], ['allowed_classes' => false]);
+
+$_EXTKEY = 'foo';
+call_user_func(static function () use($_EXTKEY) {
+    $_EXTCONF = isset($GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf'][$_EXTKEY]) ? unserialize($GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf'][$_EXTKEY], ['allowed_classes' => false]) : [];
+});
+
+?>
+-----
+<?php
+
+use TYPO3\CMS\Core\Utility\GeneralUtility;
+
+use TYPO3\CMS\Core\Configuration\ExtensionConfiguration;
+$extensionConfiguration2 = GeneralUtility::makeInstance(ExtensionConfiguration::class)->get('foo');
+$_EXTKEY = 'foo';
+call_user_func(static function () use($_EXTKEY) {
+    $_EXTCONF = isset($GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf'][$_EXTKEY]) ? GeneralUtility::makeInstance(ExtensionConfiguration::class)->get($_EXTKEY) : [];
+});
+
+?>
diff --git a/tests/Rector/v9/v0/UseExtensionConfigurationApi/UseExtensionConfigurationApiRectorTest.php b/tests/Rector/v9/v0/UseExtensionConfigurationApi/UseExtensionConfigurationApiRectorTest.php
new file mode 100644
index 000000000..106ba8c1e
--- /dev/null
+++ b/tests/Rector/v9/v0/UseExtensionConfigurationApi/UseExtensionConfigurationApiRectorTest.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ssch\TYPO3Rector\Tests\Rector\v9\v0\UseExtensionConfigurationApi;
+
+use Iterator;
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+use Ssch\TYPO3Rector\Rector\v9\v0\UseExtensionConfigurationApiRector;
+use Symplify\SmartFileSystem\SmartFileInfo;
+
+final class UseExtensionConfigurationApiRectorTest extends AbstractRectorTestCase
+{
+    /**
+     * @dataProvider provideDataForTest()
+     */
+    public function test(SmartFileInfo $fileInfo): void
+    {
+        $this->doTestFileInfo($fileInfo);
+    }
+
+    public function provideDataForTest(): Iterator
+    {
+        return $this->yieldFilesFromDirectory(__DIR__ . '/Fixture');
+    }
+
+    protected function getRectorClass(): string
+    {
+        return UseExtensionConfigurationApiRector::class;
+    }
+}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 78bf53987..ea675c173 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -38,6 +38,7 @@
 $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['password'] = 'password';
 $GLOBALS['TYPO3_CONF_VARS']['DB']['Connections']['Default']['host'] = 'host';
 $GLOBALS['TYPO3_CONF_VARS']['BE']['fileDenyPattern'] = FileNameValidator::DEFAULT_FILE_DENY_PATTERN;
+$GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['foo'] = 'a:6:{s:9:"loginLogo";s:8:"logo.jpg";s:19:"loginHighlightColor";s:7:"#000000";s:20:"loginBackgroundImage";s:8:"logo.jpg";s:13:"loginFootnote";s:8:"Footnote";s:11:"backendLogo";s:0:"";s:14:"backendFavicon";s:0:"";}';
 
 define('TYPO3_MODE', 'BE');
 define('TYPO3_URL_MAILINGLISTS', 'http://lists.typo3.org/cgi-bin/mailman/listinfo');