wp-includes/functions.php in WordPress before 3.6.1 does not properly determine whether data has been serialized, which allows remote attackers to execute arbitrary code by triggering erroneous PHP unserialize operations.
codex.wordpress.org/Version_3.6.1
core.trac.wordpress.org/changeset/25325
lists.fedoraproject.org/pipermail/package-announce/2013-September/116828.html
lists.fedoraproject.org/pipermail/package-announce/2013-September/116832.html
lists.fedoraproject.org/pipermail/package-announce/2013-September/117118.html
wordpress.org/news/2013/09/wordpress-3-6-1/
www.debian.org/security/2013/dsa-2757