Pastry is a popular DHT overlay for its capability to facilitate storage and retrieval of data/ file among large number of nodes, efficiently without any centralized server. Performance is one of the major concerns in such networks. This work, frames a collaborative attack against Pastry named CAP to reduce the performance. Malicious nodes in CAP, intelligently poison the routing tables by sending fake state-table update messages to a target node. The malicious nodes drop (or forwards to another malicious node) the look-up requests received from a peer. Impact of CAP is observed and found to be significant degradation in performance. Further, we propose a defense mechanism to reduce the effects of such attack.