The _expand_quoted_text function in libs/Smarty_Compiler.class.php in Smarty 2.6.20 r2797 and earlier allows remote attackers to execute arbitrary PHP code via vectors related to templates and a \ (backslash) before a dollar-sign character.
https://exchange.xforce.ibmcloud.com/vulnerabilities/46406
http://www.securityfocus.com/bid/31862
http://www.openwall.com/lists/oss-security/2008/10/25/2
http://www.debian.org/security/2008/dsa-1691