WordPress 2.1.1, as downloaded from some official distribution sites during February and March 2007, contains an externally introduced backdoor that allows remote attackers to execute arbitrary commands via (1) an eval injection vulnerability in the ix parameter to wp-includes/feed.php, and (2) an untrusted passthru call in the iz parameter to wp-includes/theme.php.
secunia.com/advisories/24374
wordpress.org/development/2007/03/upgrade-212/
www.kb.cert.org/vuls/id/214480
www.kb.cert.org/vuls/id/641456
www.securityfocus.com/archive/1/461794/100/0/threaded
www.securityfocus.com/bid/22797
www.vupen.com/english/advisories/2007/0812
exchange.xforce.ibmcloud.com/vulnerabilities/32804
exchange.xforce.ibmcloud.com/vulnerabilities/32807
ifsec.blogspot.com/2007/03/wordpress-code-compromised-to-enable.html