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, POST /api/v1/estimates/{estimate}/convert-to-invoice in ConvertEstimateController authorizes only the caller's create-invoice ability and does not authorize access to the route-bound Estimate. Because route-model binding can resolve an estimate from any company, an authenticated user with create-invoice ability can copy another company's line items, prices, totals, taxes, notes, currency, and customer data into an invoice in the attacker's company. The victim company's configured conversion action reaches checkForEstimateConvertAction and can also change or delete the original estimate. This issue is fixed in version 2.4.0.