wp-admin/upgrade.php in WordPress, probably 2.6.x, allows remote attackers to upgrade the application, and possibly cause a denial of service (application outage), via a direct request.
https://exchange.xforce.ibmcloud.com/vulnerabilities/50384
https://euvd.enisa.europa.eu/vulnerability/EUVD-2008-6727
http://www.debian.org/security/2009/dsa-1871
http://archives.neohapsis.com/archives/bugtraq/2008-12/0226.html