Formal State-Machine Verification for Preventing Step-Skipping, Negative-Quantity Logic, and Flow Automation
A checkout or transfer workflow consists of three steps, and an attacker jumps straight from step one to step three to skip payment verification, or enters a negative quantity to credit their own balance. The verifier tests state-transition invariants on synthetic fixtures and compiles a strict state-machine contract for border enforcement.
Business logic and sensitive flow vulnerabilities occur when each individual endpoint is syntactically valid and authenticated, yet the application fails to enforce the required sequence of state transitions or domain value invariants across a multi-step transaction. Attackers exploit these gaps by skipping intermediate verification steps, submitting negative quantities or zero-value rounding amounts, replaying completed workflow tokens, or automating high-velocity inventory reservation.
Security Officer (Plain Meaning): Halts "Commit negative-quantity ledger settlement or exhaust live inventory reservations" before socket (0 live DB damage, signed GOST receipt)
IT Auditor & SecOps (Evidence): Scope OWASP API6:2023 (Sensitive Business Flows) | Wire Rule SEC-ZD-V2-11 | Formal Witness e412b750c8391a08
Technocrat, CTO & VC (Moat): Z3 Invariant (assert (and (= (step_predecessor_verified state_machine c... | FP = 0.0% | Contract IMMUNE-BFA-E412B750 (mcp-sentinel 1.1.2)1. In-Path Interception and Contract Synthesis Schematic for API-BFA-11
Deterministic verification flow for API-BFA-11 (OWASP API6:2023 (Sensitive Business Flows), OWASP OAT-007 / OAT-015 / CWE-799): wire filter SEC-ZD-V2-11 intercepts destructive mutations prior to socket delivery, formal witness e412b750c8391a08 proves the flaw, and compiler emits gateway rule IMMUNE-BFA-E412B750 for mcp-sentinel.
2. Zero-Damage Wire Filtering and Formal Solver Invariant for API-BFA-11
Under rule SEC-ZD-V2-11, the in-path software filter confines business-flow probes to synthetic sandbox transactions and blocks any state commit affecting real inventory, payment gateways, or customer ledgers before socket transmission.
On the benchmark stand, the verifier executes out-of-order transition probes and boundary-value mutations against vulnerable handlers and state-enforced decoy routes. Confirming an illegal transition or negative-value acceptance produces formal witness e412b750c8391a08 with zero false positives.
Class Identifier: API-BFA-11 (api_business_flow_abuse)
Taxonomy Concordance: OWASP API6:2023 (Sensitive Business Flows) | OWASP OAT-007 / OAT-015 / CWE-799
Execution Mode: Active Safe Probing (AUTO_SCAN)
Candidate Probe: POST /api/v1/checkout/confirm {"step":"final_settlement","skip_verification":true,"quantity":-5,"unit_price":1000}
Blocked Mutation: Commit negative-quantity ledger settlement or exhaust live inventory reservations
Z3 Solver Invariant: (assert (and (= (step_predecessor_verified state_machine call) true) (> (item_quantity call) 0) (<= (actor_flow_rate call) threshold)))
Wire Sandbox Rule: SEC-ZD-V2-11
Formal Witness Hash: e412b750c8391a08
Compiled Sentinel Rule: IMMUNE-BFA-E412B750 (mcp-sentinel 1.1.2)3. Autonomous Synthesis of Gateway Contract IMMUNE-BFA-E412B750 and Streebog-256 Receipt
From witness e412b750c8391a08, the compiler synthesizes contract IMMUNE-BFA-E412B750 for border enforcement. The rule enforces a cryptographic finite-state machine over session transitions, validates strict positive numerical domains, and applies per-principal velocity budgets inside mcp-sentinel.
4. Engineering Reference Notes for API-BFA-11
Why traditional signature firewalls cannot detect business logic bypass
A business logic probe contains clean, well-formed JSON without a single SQL quote or script tag; catching it requires verifying the mathematical invariant of the transaction state graph and numeric domain constraints.
Enforcing multi-step workflow order at the stateless proxy layer
Each completed workflow step issues a compact Streebog-256 state receipt that must be presented and verified before the proxy permits invocation of the next transition endpoint.