InvoiceShelf is an open-source web & mobile app that helps track expenses, payments and create professional invoices and estimates. Prior to version 2.2.0, a Server-Side Request Forgery (SSRF) vulnerability exists in the Payment receipt PDF generation module. User-supplied HTML in the payment Notes field is passed unsanitised to the Dompdf rendering library, which will fetch any remote resources referenced in the markup. The vulnerability is exploitable directly via the PDF receipt endpoint, regardless of whether automated email attachments are enabled. This issue has been patched in version 2.2.0.