Kimai 2.56.0 contains a server-side request forgery vulnerability in its invoice PDF preview and generation workflow. If an attacker can control Markdown content that is later rendered into an invoice PDF, such as "Customer.invoiceText", the server-side PDF renderer will fetch remote image URLs embedded in Markdown image syntax. This allows the application server to issue outbound requests to attacker-controlled or internal targets during PDF rendering. The behavior can be used for internal network probing, server-side reachability checks, and potentially follow-on exploitation depending on deployment environment and accessible internal services.