diff --git a/lib/private/AppFramework/Middleware/Security/CORSMiddleware.php b/lib/private/AppFramework/Middleware/Security/CORSMiddleware.php
index af6d3de657..bcbbc04f7c 100644
--- a/lib/private/AppFramework/Middleware/Security/CORSMiddleware.php
+++ b/lib/private/AppFramework/Middleware/Security/CORSMiddleware.php
@@ -83,14 +83,13 @@ class CORSMiddleware extends Middleware {
 	public function beforeController($controller, $methodName) {
 		// ensure that @CORS annotated API routes are not used in conjunction
 		// with session authentication since this enables CSRF attack vectors
-		if ($this->reflector->hasAnnotation('CORS') &&
-			!$this->reflector->hasAnnotation('PublicPage')) {
-			$user = $this->request->server['PHP_AUTH_USER'];
-			$pass = $this->request->server['PHP_AUTH_PW'];
+		if ($this->reflector->hasAnnotation('CORS') && !$this->reflector->hasAnnotation('PublicPage')) {
+			$user = array_key_exists('PHP_AUTH_USER', $this->request->server) ? $this->request->server['PHP_AUTH_USER'] : null;
+			$pass = array_key_exists('PHP_AUTH_PW', $this->request->server) ? $this->request->server['PHP_AUTH_PW'] : null;
 
 			$this->session->logout();
 			try {
-				if (!$this->session->logClientIn($user, $pass, $this->request, $this->throttler)) {
+				if ($user === null || $pass === null || !$this->session->logClientIn($user, $pass, $this->request, $this->throttler)) {
 					throw new SecurityException('CORS requires basic auth', Http::STATUS_UNAUTHORIZED);
 				}
 			} catch (PasswordLoginForbiddenException $ex) {