Ticket #33475: 33475.patch

wp-includes/cron.php

@@ -23 +23 @@
 function wp_schedule_single_event( $timestamp, $hook, $args = array()) {
         // don't schedule a duplicate if there's already an identical event due within 10 minutes of it
         $next = wp_next_scheduled($hook, $args);
-        if ( $next && abs( $next - $timestamp ) <= 10 * MINUTE_IN_SECONDS ) {
+        if ( ( ! is_numeric( $timestamp ) || $timestamp <= 0 ) || ( $next && abs( $next - $timestamp ) <= 10 * MINUTE_IN_SECONDS ) ) {
                 return;
         }