Hand-written deny rules for learned access control were unsound in 50-70% of checks and would have blocked 16-78% of legitimate grants
AspireAI community · arXiv (cs.CR)
Learned access control systems are usually deployed behind two hand-built pieces: a hard-deny set enforced by a trusted shield, and a region map deciding whether a request is answered by mined rules or by the learned model. Auditing either one validates neither. This work formalizes hard-deny soundness and checks it exhaustively over relations of up to 794,250 tuples across the five public ABAC Lab policies, and finds that clauses which faithfully transcribe an explicit restriction are unsound at rates of 0.50 to 0.70 depending on the elicitor — a human author and three blind language models — because prose scopes a restriction to one section while the grant relation is a disjunction over all rules; 97% of counterexamples are granted by some other rule. Shipped unchecked, those deny sets would withhold 16% to 78% of everything the policies grant. The limitation is scope: five public ABAC policies, and the authors note the hybrid-versus-learner comparison gives opposite verdicts depending on which loss you measure.
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