The cognitive radio enabled IEEE 802.22 wireless regional area network (WRAN) is designed to opportunistically utilize the unused or under-utilized TV bands. However, due to the lack of proactive security protocols and proper interaction policies among the secondary networks themselves, the IEEE 802.22 networks are vulnerable to various denial-of-service (DoS) threats. In this paper, we study the impact of coordinated DoS attacks on IEEE 802.22 networks from the malicious nodes' perspective. Assuming that multiple malicious nodes will launch coordinated attacks, we formulate a cooperative game among the malicious nodes. The expression of the net payoff is derived and the optimal decision strategy for the malicious nodes is obtained numerically. Simulation results demonstrate that the coordinated attack approach can enhance as high as 10-15% more net payoff for the malicious nodes than the uncoordinated attack.