diff --git a/CHANGELOG.md b/CHANGELOG.md
index 90e532c..f47bdb9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## Changelog
 
+* 5.3.1 - 2026-06-08 - Added restrict access check for MultiSites.getAll report for non superusers
 * 5.3.0 - 2026-05-11 - Added alert description and helptexts
 * 5.2.6 - 2026-04-27 - Updated API documentation
 * 5.2.5 - 2026-03-30 - Added escaping for report_matched value
diff --git a/Processor.php b/Processor.php
index 6fcdf7a..6ca1349 100755
--- a/Processor.php
+++ b/Processor.php
@@ -248,6 +248,8 @@ public function getValueForAlertInPast($alert, $idSite, $subPeriodN)
             $params = array_merge($params, $report['parameters']);
         }
 
+        $params = $this->restrictMultiSitesReportToAlertOwner($params, $report, $alert);
+
         $subtableId = DataTable\Manager::getInstance()->getMostRecentTableId();
 
         $table = ApiRequest::processRequest($report['module'] . '.' . $report['action'], $params, $default = []);
@@ -264,6 +266,22 @@ public function getValueForAlertInPast($alert, $idSite, $subPeriodN)
         return $value;
     }
 
+    protected function restrictMultiSitesReportToAlertOwner(array $params, array $report, array $alert): array
+    {
+        if (
+            $report['module'] !== 'MultiSites'
+            || $report['action'] !== 'getAll'
+            || empty($alert['login'])
+            || Piwik::hasTheUserSuperUserAccess($alert['login'])
+        ) {
+            return $params;
+        }
+
+        $params['_restrictSitesToLogin'] = $alert['login'];
+
+        return $params;
+    }
+
     /**
      * Checks whether the archive status is complete. We throw an exception if the status is something other than
      * complete. If no status is found, we do nothing.
diff --git a/phpstan/phpstan.modified.neon b/phpstan/phpstan.modified.neon
index 1cd88df..ddb9ff9 100644
--- a/phpstan/phpstan.modified.neon
+++ b/phpstan/phpstan.modified.neon
@@ -2,4 +2,5 @@ includes:
     - ../phpstan.neon
 parameters:
     level: 5
-    tmpDir: /tmp/phpstan/CustomAlerts/modified
\ No newline at end of file
+    tmpDir: /tmp/phpstan/CustomAlerts/modified
+    treatPhpDocTypesAsCertain: false
diff --git a/plugin.json b/plugin.json
index d0a992b..d9bec1d 100644
--- a/plugin.json
+++ b/plugin.json
@@ -1,7 +1,7 @@
 {
     "name": "CustomAlerts",
     "description": "Create custom Alerts to be notified of important changes on your website or app! ",
-    "version": "5.3.0",
+    "version": "5.3.1",
     "require": {
         "matomo": ">=5.0.0-b1,<6.0.0-b1"
     },
diff --git a/tests/Integration/ProcessorTest.php b/tests/Integration/ProcessorTest.php
index 11b34da..38e63fc 100644
--- a/tests/Integration/ProcessorTest.php
+++ b/tests/Integration/ProcessorTest.php
@@ -68,6 +68,11 @@ public function shouldBeTriggered($alert, $metricOne, $metricTwo)
     {
         return parent::shouldBeTriggered($alert, $metricOne, $metricTwo);
     }
+
+    public function restrictMultiSitesReportToAlertOwner(array $params, array $report, array $alert): array
+    {
+        return parent::restrictMultiSitesReportToAlertOwner($params, $report, $alert);
+    }
 }
 
 /**
@@ -619,6 +624,39 @@ public function test_processAlert_shouldOnlyBeTriggeredIfAlertMatches()
         $processorMock->processAlert($alert, 1);
     }
 
+    public function test_restrictMultiSitesReportToAlertOwner_shouldRestrictMultiSitesGetAllForAlertOwner()
+    {
+        $params = $this->processor->restrictMultiSitesReportToAlertOwner(
+            [],
+            ['module' => 'MultiSites', 'action' => 'getAll'],
+            ['login' => 'aUser']
+        );
+
+        $this->assertSame('aUser', $params['_restrictSitesToLogin']);
+    }
+
+    public function test_restrictMultiSitesReportToAlertOwner_shouldNotRestrictSuperUserAlertOwner()
+    {
+        $params = $this->processor->restrictMultiSitesReportToAlertOwner(
+            [],
+            ['module' => 'MultiSites', 'action' => 'getAll'],
+            ['login' => 'superUserLogin']
+        );
+
+        $this->assertArrayNotHasKey('_restrictSitesToLogin', $params);
+    }
+
+    public function test_restrictMultiSitesReportToAlertOwner_shouldNotRestrictOtherReports()
+    {
+        $params = $this->processor->restrictMultiSitesReportToAlertOwner(
+            [],
+            ['module' => 'VisitsSummary', 'action' => 'get'],
+            ['login' => 'aUser']
+        );
+
+        $this->assertArrayNotHasKey('_restrictSitesToLogin', $params);
+    }
+
     public function test_shouldBeTriggered_ShouldFail_IfInvalidConditionGiven()
     {
         $this->expectException(\Exception::class);