artmedic newsletter 4.1 and possibly other versions, when register_globals is enabled, allows remote attackers to modify arbitrary files and execute arbitrary PHP code via the logfile parameter in a direct request to log.php, which causes the $logfile variable to be redefined to an attacker-controlled value, as demonstrated by injecting PHP code into info.php.
https://exchange.xforce.ibmcloud.com/vulnerabilities/26597
http://www.vupen.com/english/advisories/2006/1930
http://www.securityfocus.com/archive/1/434738/100/0/threaded