CVE-2026-73829 - Non-atomic hash-credential dedup in mpp Tempo allows replay of a confirmed payment under a concurrent race
Brief
CVE ID : CVE-2026-73829
Published : Aug. 19, 2026, 6:17 p. m.
- 51 minutes ago
Description : 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.