The vulnerability allows user‑supplied, unsanitised HTML in the Notes field of an invoice to be rendered by the Dompdf library, which can fetch any remote resources referenced in the markup. This permits an attacker to force the server to make arbitrary outbound HTTP requests to internal or external addresses, potentially exposing sensitive data, accessing privileged services, or facilitating further attacks. The weakness corresponds to the Server‑Side Request Forgery category (CWE‑918).

Invoices managed using the open‑source InvoiceShelf application are affected when running any version earlier than 2.2.0. The problem is resolved in the 2.2.0 release, as indicated by the vendor’s security advisory.

The CVSS score of 7.6 assigns this issue a high severity rating, while an EPSS score below 1% suggests a low probability of spontaneous exploitation in current threat data. It is not listed in the CISA Known Exploited Vulnerabilities catalog. The description implies that the attack vector would involve accessing the PDF preview or email sending endpoints, though any authentication or permission prerequisites are not explicitly documented.