{"id":"EEF-CVE-2026-73829","summary":"Non-atomic hash-credential dedup in mpp Tempo allows replay of a confirmed payment under a concurrent race","details":"## Summary\n\nTime-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.\n\nThe `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.\n\nThis issue affects mpp: from 0.2.0 before 0.6.1.\n\n## Configurations\n\nThe race is only reachable when `MPP.Methods.Tempo` is configured with a dedup store (`\"store\"` in `method_config`). The default is `nil`, which runs the library statelessly and provides no application-level replay protection at all, a documented property rather than part of this issue.","aliases":["CVE-2026-73829","GHSA-w8j7-7qc3-5f24"],"modified":"2026-09-08T05:45:02.680456301Z","published":"2026-08-19T17:19:43.696Z","database_specific":{"cpe_ids":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-367"],"capec_ids":["CAPEC-29"]},"references":[{"type":"ADVISORY","url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-w8j7-7qc3-5f24"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-73829.html"},{"type":"FIX","url":"https://github.com/ZenHive/mpp/commit/46c5b0e1311da7d92190dc7d9ea89027a1d365e9"},{"type":"PACKAGE","url":"https://hex.pm/packages/mpp"}],"affected":[{"package":{"name":"mpp","ecosystem":"Hex","purl":"pkg:hex/mpp"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.2.0"},{"fixed":"0.6.1"}]}],"versions":["0.2.0","0.3.0","0.3.1","0.3.2","0.4.0","0.6.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-73829.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/ZenHive/mpp","events":[{"introduced":"f8904666061fbab695874856d8fcd02c471dfe1b"},{"fixed":"46c5b0e1311da7d92190dc7d9ea89027a1d365e9"}]}],"versions":["v0.6.0","v0.5.1","v0.4.0","v0.3.0","v0.2.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-73829.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"}],"credits":[{"name":"Jonatan Männchen / EEF","type":"ANALYST"},{"name":"E.FU","type":"FINDER"},{"name":"E.FU","type":"REMEDIATION_DEVELOPER"}]}