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.
https://exchange.xforce.ibmcloud.com/vulnerabilities/32807
https://exchange.xforce.ibmcloud.com/vulnerabilities/32804
http://www.vupen.com/english/advisories/2007/0812
http://www.securityfocus.com/bid/22797
http://www.securityfocus.com/archive/1/461794/100/0/threaded
http://www.kb.cert.org/vuls/id/641456
http://www.kb.cert.org/vuls/id/214480