The Electronic Product Code Generation 2 (EPC Gen2) is an international standard that proposes the use of Radio Frequency IDentification (RFID) in the supply chain. It is designed to balance cost and functionality. As a consequence, security on board of EPC Gen2 tags is often minimal. It is, indeed, mainly based on the use of on board pseudorandomness, used to obscure the communication between readers and tags; and to acknowledge the proper execution of password-protected operations. In this paper, the authors present a practical implementation attack on a weak Pseudo-Random Number Generator (PRNG) designed specifically for EPC Gen2 tags.