This paper introduces a possibility for attackers to acquire the keyboard scan codes through using the RESEND command provided by the keyboard hardware itself, based on the PS/2 interface that is a dominant interface for input devices. Accordingly, a keyboard sniffing program using the introduced vulnerability is implemented to prove the severeness of the vulnerability, which shows that user passwords can be easily exposed. As one of the intrinsic vulnerabilities found on the existing platforms, for which there were little considerations on the security problems when they were designed, it is required to consider a hardware approach to countermeasure the introduced vulnerability.