Attack Surface Evolution in Multi-Agent Systems: WebMASLab and the Telephone Loop Exploit
The transition from monolithic Single-Agent Systems (SAS) to Multi-Agent Systems (MAS) introduces critical "structural attack surfaces" derived from inter-agent delegation and interaction logic. Using the WebMASLab framework, researchers have identified the "Telephone Loop" exploit, a mechanism that leverages cross-agent delegation to trigger recursive, resource-exhausting task cycles. Empirical testing against frontier models, including GPT-5.2 and Claude Sonnet 4.5, demonstrates an 80% average attack success rate (ASR) at baseline. Current defenses, such as prompt-hardening, exhibit non-linear efficacy and fail to provide generalized protection, leaving distributed agentic architectures vulnerable to systemic failure and resource exhaustion.