As adversarial techniques constantly evolve to circumvent existing security measures, an isolated, stand-alone intrusion detection system (IDS) is unlikely to be efficient or effective. Hence, there has been a trend towards developing collaborative intrusion detection networks (CIDNs), where IDS nodes collaborate and communicate with each other. Such a distributed ecosystem can achieve improved detection accuracy, particularly for detecting emerging threats in a timely fashion (before the threat becomes common knowledge). However, there are inherent limitations due to malicious insiders who can seek to compromise and poison the ecosystem. A potential mitigation strategy is to introduce a challenge-based trust mechanism, in order to identify and penalize misbehaving nodes by evaluating the satisfaction between challenges and responses. While this mechanism has been shown to be robust against common insider attacks, it may still be vulnerable to advanced insider attacks in a real-world deployment. Therefore, in this paper, we develop a collusion attack, hereafter referred to as Bayesian Poisoning Attack, which enables a malicious node to model received messages and to craft a malicious response to those messages whose aggregated appearance probability of normal requests is above the defined threshold. In the evaluation, we explore the attack performance under both simulated and real network environments. Experimental results demonstrate that the malicious nodes under our attack can successfully craft and send untruthful feedback while maintaining their trust values.