Fixes #45406 - Patch by oleg dot grenrus at dynamoid dot com

ext/session/session.c

@@ -1877,14 +1877,24 @@ static PHP_RINIT_FUNCTION(session)
 		if (value) {
 			PS(mod) = _php_find_ps_module(value TSRMLS_CC);
 		}
+	}
+
+	if (PS(serializer) == NULL) {
+		char *value;
 
-		if (!PS(mod)) {
-			/* current status is unusable */
-			PS(session_status) = php_session_disabled;
-			return SUCCESS;
+		value = zend_ini_string("session.serialize_handler", sizeof("session.serialize_handler"), 0);
+		if(value) {
+			PS(serializer) = _php_find_ps_serializer(value TSRMLS_CC);
 		}
 	}
 
+	if (PS(mod) == NULL || PS(serializer) == NULL) {
+		/* current status is unusable */
+		PS(session_status) = php_session_disabled;
+
+		return SUCCESS;
+	}
+
 	if (PS(auto_start)) {
 		php_session_start(TSRMLS_C);
 	}