The _expand_quoted_text function in libs/Smarty_Compiler.class.php in Smarty 2.6.20 before r2797 allows remote attackers to execute arbitrary PHP code via vectors related to templates and (1) a dollar-sign character, aka "php executed in templates;" and (2) a double quoted literal string, aka a "function injection security hole." NOTE: each vector affects slightly different SVN revisions.

More... (http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2008-4810)