Deterministic Single-Packet Concurrency Probing and Idempotency Lock Synthesis
An attacker sends ten identical withdrawal or coupon-redemption requests in a single parallel burst so all ten pass the balance check before the first deduction is saved. The verifier tests concurrency serialization on an isolated counter fixture and compiles an atomic idempotency and mutex rule for border enforcement.
Check-to-use concurrency (TOCTOU) race conditions arise when an application reads a balance, quota, or one-time token status in one step and commits the state update in a separate step without row-level locking or serializable transaction isolation. By multiplexing parallel requests inside a single network packet, an adversary forces multiple worker threads through the validation gate simultaneously.
Security Officer (Plain Meaning): Halts "Execute unisolated double-spend balance withdrawal or duplicate ledger write on production tables" before socket (0 live DB damage, signed GOST receipt)
IT Auditor & SecOps (Evidence): Scope OWASP API6:2023 / CWE-367 | Wire Rule SEC-ZD-V2-03 | Formal Witness 4c91e720b38d51a6
Technocrat, CTO & VC (Moat): Z3 Invariant (assert (forall ((t1 Tx) (t2 Tx)) (=> (and (= (resource_ke... | FP = 0.0% | Contract IMMUNE-RAC-4C91E720 (mcp-sentinel 1.1.2)1. In-Path Interception and Contract Synthesis Schematic for API-RAC-03
Deterministic verification flow for API-RAC-03 (OWASP API6:2023 / CWE-367, CAPEC-29 / TOCTOU): wire filter SEC-ZD-V2-03 intercepts destructive mutations prior to socket delivery, formal witness 4c91e720b38d51a6 proves the flaw, and compiler emits gateway rule IMMUNE-RAC-4C91E720 for mcp-sentinel.
2. Zero-Damage Wire Filtering and Formal Solver Invariant for API-RAC-03
Under rule SEC-ZD-V2-03, the in-path software filter restricts concurrency probes strictly to synthetic counter fixtures and blocks parallel state mutations targeting live financial or inventory tables before bytes leave the test runner.
On the benchmark stand, the verifier dispatches synchronized barrier probes against vulnerable non-locking handlers and serializable decoy routes. Observing a state counter increment beyond the permitted single-use invariant produces formal witness 4c91e720b38d51a6 with zero false positives.
Class Identifier: API-RAC-03 (race_conditions_toctou)
Taxonomy Concordance: OWASP API6:2023 / CWE-367 | CAPEC-29 / TOCTOU
Execution Mode: Active Safe Probing (AUTO_SCAN)
Candidate Probe: POST /api/v1/coupons/redeem [HTTP/2 Single-Packet Parallel Burst x16, idempotency_key: missing, code: "PROMO_ONCE_500"]
Blocked Mutation: Execute unisolated double-spend balance withdrawal or duplicate ledger write on production tables
Z3 Solver Invariant: (assert (forall ((t1 Tx) (t2 Tx)) (=> (and (= (resource_key t1) (resource_key t2)) (overlapping_window t1 t2)) (= (serialized_mutex_acquired t1 t2) true))))
Wire Sandbox Rule: SEC-ZD-V2-03
Formal Witness Hash: 4c91e720b38d51a6
Compiled Sentinel Rule: IMMUNE-RAC-4C91E720 (mcp-sentinel 1.1.2)3. Autonomous Synthesis of Gateway Contract IMMUNE-RAC-4C91E720 and Streebog-256 Receipt
From witness 4c91e720b38d51a6, the compiler synthesizes contract IMMUNE-RAC-4C91E720 for border enforcement. The contract enforces mandatory Idempotency-Key headers and per-subject in-memory mutex serialization inside mcp-sentinel before forwarding state-changing requests.
4. Engineering Reference Notes for API-RAC-03
Detection of narrow concurrency race windows using single-packet synchronization
The test runner aligns final request frames on a local barrier so they arrive at the application socket in a single synchronized batch, exposing missing transaction locks without flooding the network.
Gateway-level protection when legacy backend code lacks database row locks
The compiled gateway rule serializes concurrent write requests for the same principal and resource key in memory, rejecting duplicate in-flight mutations at the gateway boundary.