{"id":"CVE-2026-73829","summary":"Non-atomic hash-credential dedup in mpp Tempo allows replay of a confirmed payment under a concurrent race","details":"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.\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.","aliases":["EEF-CVE-2026-73829","GHSA-w8j7-7qc3-5f24"],"modified":"2026-08-20T03:55:12.341251497Z","published":"2026-08-19T17:19:43.696Z","database_specific":{"cwe_ids":["CWE-367"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73829.json","unresolved_ranges":[{"extracted_events":[{"introduced":"f8904666061fbab695874856d8fcd02c471dfe1b"},{"fixed":"46c5b0e1311da7d92190dc7d9ea89027a1d365e9"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"EEF"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-73829.html"},{"type":"WEB","url":"https://github.com"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73829.json"},{"type":"PACKAGE","url":"https://github.com/ZenHive/mpp"},{"type":"FIX","url":"https://github.com/ZenHive/mpp/commit/46c5b0e1311da7d92190dc7d9ea89027a1d365e9"},{"type":"ADVISORY","url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-w8j7-7qc3-5f24"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73829"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-73829"},{"type":"WEB","url":"https://repo.hex.pm"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/zenhive/mpp","events":[{"introduced":"7ca7538f05959a98e0e5e63e4bd949b4f362cf8d"},{"fixed":"542a525563c2fcedd670b593437deca81c6797a4"}],"database_specific":{"extracted_events":[{"introduced":"0.2.0"},{"fixed":"0.6.1"}],"source":"AFFECTED_FIELD"}}],"versions":["v0.6.0","v0.5.1","v0.4.0","v0.3.0","v0.2.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/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"}]}