KSeF is Poland’s national e-invoicing system for exchanging structured electronic invoices. Instead of sending a free-form PDF or email attachment, businesses submit invoices in a standardized machine-readable format. That format can include tax identifiers, company details, line items, payment references, and other metadata that supports automated accounting and tax reporting.
In cyber security, KSeF matters because it concentrates high-value business data in one workflow. Attackers may try to steal invoice records, abuse API credentials, or impersonate suppliers and customers using legitimate-looking invoice data. The same structure that helps automation also helps fraudsters build convincing phishing lures and payment diversion scams. Defenders reduce risk by protecting API keys and certificates, enforcing strong authentication, monitoring invoice submissions and exports, validating data integrity, and separating invoicing access from general user accounts. In practice, KSeF security is about both confidentiality and trust: if invoice data is altered or exposed, the financial and legal impact can spread well beyond the billing team.