CVE-2026-73829Low· 3.7▾ SunlitTime-of-check Time-of-use (TOCTOU) Race Condition in ZenHive mpp allows an unauthenticated remote client to redeem one confirmed on-chain payment for multiple paid-resource accesses. The type="hash" credential path in MPP.Methods.Tempo.…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 20.4 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Sep 10.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.2%
0.2% → 0.3%
Time-of-check Time-of-use (TOCTOU) Race Condition in ZenHive mpp allows an unauthenticated remote client to redeem one confirmed on-chain payment for multiple paid-resource accesses.
The type="hash" credential path in MPP.Methods.Tempo.verify/2 guards against replay with a non-atomic check-then-mark sequence: check_hash_unused/2 reads the dedup store, an eth_getTransactionReceipt round trip verifies the payment on chain, and only then does mark_hash_used/2 write the mark. Concurrent requests carrying the same settled payment hash all pass the read before any of them writes, so each is issued a receipt. The store's atomic check_and_mark/2 primitive is available and used by the type="transaction" path, but the hash path calls plain get and put even when the configured store implements it. Exploitation requires a dedup store to be configured; the default nil store is stateless and documented as offering no replay protection at all.
This issue affects mpp: from 0.2.0 before 0.6.1.
machine_payments_protocol >= 0.2.0, < 0.6.1Upgrade past the affected range:
machine_payments_protocol 0.6.1Connected by shared product, vendor, weakness, or advisory.
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