Kimai is an open-source time tracking application. Versions prior to 2.58.0 contain a server-side request forgery vulnerability in their 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. Version 2.58.0 patches the issue.