LEX Baza Dokumentów is vulnerable to DOM-based XSS in "em" cookie parameter. The application unsafely processes the parameter on the client side, allowing an attacker to execute arbitrary JavaScript in the context of the victim's browser. An attacker with ability to set a cookie can perform a more severe attack, so we evaluate the impact and risk of exploitation as minimal. However, the vendor considered this a vulnerability and released a security patch. This issue was fixed in version 1.3.4.