Dynamic variable evaluation vulnerability in index.php in Stadtaus Guestbook Script 1.7 and earlier, when register_globals is enabled, allows remote attackers to modify arbitrary program variables via parameters, which are evaluated as PHP variable variables, as demonstrated by performing PHP remote file inclusion using the include_files array parameter.
https://exchange.xforce.ibmcloud.com/vulnerabilities/26252
http://www.vupen.com/english/advisories/2006/1660
http://www.stadtaus.com/forum/t-2600.html
http://www.securityfocus.com/bid/17845