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EEF-CVE-2026-73136
Summary
Authentication Bypass by Capture-replay in ZenHive mpp allows an unauthenticated third party to obtain paid resources by replaying a transfer settled by an unrelated payer.
MPP.Methods.Tempo normally binds a settled TIP-20 TransferWithMemo to the specific challenge under verification through an attribution nonce carried in the memo. When a static "memo" is configured in method_config, check_matched_memo_binding/3 returns the match unconditionally and that binding is skipped, leaving only token, recipient, amount and the static memo value to match on. The static memo is echoed in every unauthenticated 402 response and Tempo transfers are public, so an attacker can take any matching transfer paid by a legitimate customer, request a fresh challenge for the same route, and present that transaction hash as a type="hash" credential. The hash path performs no sender or signature check tying the presenter to the wallet that broadcast the transfer.
This issue affects mpp: from 0.6.1 before 0.6.4.
Workaround
Remove the static "memo" from the Tempo method_config so verification falls back to the default per-challenge attribution binding, which ties each settled transfer to the challenge being verified. Where a static memo must be kept, configure a dedup store (for example MPP.Tempo.ConCacheStore) with a TTL at least as long as the challenge expiry, which reduces unlimited replay to a race on the transaction hash rather than closing it.
Configuration
Only deployments that configure a static "memo" in the Tempo method_config are affected. Deployments using the default per-challenge attribution memo are not: that path binds each settled transfer to the challenge under verification and is single-use by construction.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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