wp-trackback.php in WordPress 2.0.6 and earlier does not properly unset variables when the input data includes a numeric parameter with a value matching an alphanumeric parameter's hash value, which allows remote attackers to execute arbitrary SQL commands via the tb_id parameter. NOTE: it could be argued that this vulnerability is due to a bug in the unset PHP command (CVE-2006-3017) and the proper fix should be in PHP; if so, then this should not be treated as a vulnerability in WordPress.
https://www.exploit-db.com/exploits/3109
https://exchange.xforce.ibmcloud.com/vulnerabilities/31385