DebugKit provides a debugging toolbar for CakePHP applications. Prior to 4.10.3 and 5.2.4, the DebugKit MailPreview feature in src/Controller/MailPreviewController.php accepts a route-controlled previewName value in findPreview and passes the resolved class from App::className() to constructor execution without rejecting namespace separators or verifying that the class extends DebugKit\Mailer\MailPreview. An attacker able to access DebugKit while debug mode is enabled and the request hostname is local or allowlisted can select an unintended application class through the mail-preview preview route, resulting in arbitrary constructor execution and limited disclosure of application information. This issue is fixed in versions 4.10.3 and 5.2.4.