M4 PDF plugin for Prestashop sites, in its 3.2.3 version and before, is vulnerable to an arbitrary HTML Document crafting vulnerability. The resource /m4pdf/pdf.php uses templates to dynamically create documents. In the case that the template does not exist, the application will return a fixed document with a message in mpdf format. An attacker could exploit this vulnerability by inputting a valid HTML/CSS document as the value of the parameter.