In Smarty before 3.1.47 and 4.x before 4.2.1, libs/plugins/function.mailto.php allows XSS. A web page that uses smarty_function_mailto, and that could be parameterized using GET or POST input parameters, could allow injection of JavaScript code by a user.
https://security.gentoo.org/glsa/202209-09
https://lists.debian.org/debian-lts-announce/2023/01/msg00002.html
https://github.com/smarty-php/smarty/releases/tag/v4.2.1
https://github.com/smarty-php/smarty/releases/tag/v3.1.47