Abstract: Integrated sensing and communication (ISAC) is one of the core technologies for 6G networks. It achieves efficient synergy between communication and sensing functions by sharing spectrum and hardware resources. This demonstrates its immense potential for integrated air-ground-space intelligent connectivity. However, its integrated nature introduces complex security threats. Traditional communication security mechanisms face challenges in ensuring data integrity and real-time performance for sensing systems, especially in aerospace applications where vulnerabilities may lead to severe consequences. This paper systematically analyses the vulnerability mechanisms inherent in ISAC systems. By analyzing the unique characteristics of integrated air-ground-space scenarios, we proposes a cross-layer dynamic defence framework to counter novel attack vectors. This research systematically examines the inherent conflicts in ISAC systems from the perspectives of hardware sharing, spectrum sharing, and resource competition, and reveals the vulnerability mechanisms of signal generation, data collection, and resource scheduling. It further analyzes their impact extent in aviation communication scenarios. By summarizing cross-layer collaborative attack patterns in typical integrated space-air-ground scenarios, this paper points out the limitations of traditional domain-specific defense mechanisms under spatiotemporal dynamic threats. Finally, a collaborative defense system is proposed. It integrates the trusted foundation of the physical layer, the security defense line of data semantics, and the dynamic elastic scheduling of resources. The system achieves deep integration of security mechanisms and the communication-sensing function chain. The research also looks at the technical challenges and standardisation requirements in open air-ground-space environments. This lays a preliminary theoretical foundation for the development of targeted security architectures for future 6G networks, offering preliminary references for security assurance in integrated communication-sensing applications within the aviation field.

Key words: ISAC, Air-Ground-Space Network, Endogenous Security Threats, Cross-Layer Defense, Dynamic Resilience