Communication security is a major concern in industrial process management. Indeed, in addition to real-time requirements, it is very important to ensure that sensing data sent by field sensors are not altered or modified during their transmission. This is more true in Wireless Sensor Networks where communication can be hijacked and false data injected. Therefore wireless communication protocols include several security mechanisms to ensure data confidentiality and integrity. In this paper, we present an attack against WirelessHART, the leading wireless communication protocol in industrial environment. We show that an insider attacker can bypass security mechanisms and inject false commands in the network. Such attacks can have harmful economical consequences or even more can threaten human lives. We propose also some solutions that can be applied for detecting and mitigating this kind of attacks.