The sanitize_widget_instance function in wp-includes/class-wp-customize-widgets.php in WordPress before 4.2.4 does not use a constant-time comparison for widgets, which allows remote attackers to conduct a timing side-channel attack by measuring the delay before inequality is calculated.
https://wpvulndb.com/vulnerabilities/8130
https://wordpress.org/news/2015/08/wordpress-4-2-4-security-and-maintenance-release/
https://core.trac.wordpress.org/changeset/33536
https://core.trac.wordpress.org/changeset/33535
https://codex.wordpress.org/Version_4.2.4
http://www.securitytracker.com/id/1033178
http://www.securityfocus.com/bid/76160