Yeh et al. recently have proposed a mutual authentication protocol based on EPC Class-1 Gen.-2 standard [1]. They have claimed that their protocol is secure against adversarial attacks and also provides forward secrecy. In this paper we will show that the proposed protocol does not have proper security features. A powerful and practical attack is presented on this protocol whereby the whole security of the protocol is broken. Furthermore, Yeh et al. protocol does not assure the untraceabilitiy and backward untraceabilitiy aspects. Namely, all past and next transactions of a compromised tag will be traceable by an adversary.