Labels Are Not Endpoints: Treatment Leakage and Construct Validity in MCP Agent Security Evaluation
Security evaluations of tool-using agents often equate stored labels with behavioral facts. We audit a preserved campaign by tracing 10,200 execution rows to 180 model-bound requests, 45 semantic requests, and 15 observable stimuli. Two schema treatments were delivered, but the planned external payload-family corpus was not. The historical grader exhibited direct treatment leakage: treatment metadata gated the ATTACK_SUCCESS class, so fixed behavior could change class under treatment relabeling. A treatment-blind reconstruction corrects 58 historical ATTACK_SUCCESS or HIJACK_ATTEMPT labels to authorized benign completions while preserving three verified protected-data transfers and one se...
| Authors | Rana Muhammad Ahmed, Sabahat Abbas |
|---|---|
| Primary category | cs.CR |
| Published | 13 August 2026 |
| Last updated at source | 13 August 2026 |
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