InvoiceShelf is an open-source web & mobile app that helps track expenses, payments and create professional invoices and estimates. Prior to version 2.4.0, InvoiceShelf's PDFConfigurationRequest.php validates the owner-controlled gotenberg_host setting only as a syntactically valid URL. GotenbergPDFDriver::loadView later sends a multipart HTTP request containing rendered invoice, estimate, or payment HTML as document.html to that host without rejecting private, loopback, link-local, or reserved addresses. An owner can use PDF generation to reach internal services or cloud metadata endpoints, and a configured external host receives customer names, addresses, line items, totals, and company identifiers from subsequent PDF renders. This issue is fixed in version 2.4.0.