{"id":"CVE-2026-73829","state":"PUBLISHED","title":"Non-atomic hash-credential dedup in mpp Tempo allows replay of a confirmed payment under a concurrent race","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.\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.","publishedAt":"2026-08-19T17:19:43.696Z","updatedAt":"2026-08-19T18:58:33.322Z","severity":{"score":6.3,"label":"Medium","version":"4.0","vector":"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","source":"EEF"},"assigner":"EEF","products":["ZenHive mpp"],"affected":[{"vendor":"ZenHive","product":"mpp","packageName":"mpp","packageURL":"pkg:hex/mpp","defaultStatus":"unaffected","versions":[{"version":"0.2.0","status":"affected","lessThan":"0.6.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Methods.Tempo'"],"programFiles":["lib/mpp/methods/tempo.ex"],"programRoutines":[{"name":"'Elixir.MPP.Methods.Tempo':verify/2"}],"repo":"https://github.com/ZenHive/mpp"},{"vendor":"ZenHive","product":"mpp","packageName":"zenhive/mpp","packageURL":"pkg:github/zenhive/mpp","defaultStatus":"unaffected","versions":[{"version":"f8904666061fbab695874856d8fcd02c471dfe1b","status":"affected","lessThan":"46c5b0e1311da7d92190dc7d9ea89027a1d365e9","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Methods.Tempo'"],"programFiles":["lib/mpp/methods/tempo.ex"],"programRoutines":[{"name":"'Elixir.MPP.Methods.Tempo':verify/2"}],"repo":"https://github.com/ZenHive/mpp"}],"references":["https://github.com/ZenHive/mpp/security/advisories/GHSA-w8j7-7qc3-5f24","https://cna.erlef.org/cves/CVE-2026-73829.html","https://osv.dev/vulnerability/EEF-CVE-2026-73829","https://github.com/ZenHive/mpp/commit/46c5b0e1311da7d92190dc7d9ea89027a1d365e9"],"weaknesses":["CWE-367"],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/73xxx/CVE-2026-73829.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-73829","state":"PUBLISHED","datePublished":"2026-08-19T17:19:43.696Z","dateUpdated":"2026-08-19T18:58:33.322Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-08-17T11:15:02.320Z"},"containers":{"cna":{"title":"Non-atomic hash-credential dedup in mpp Tempo allows replay of a confirmed payment under a concurrent race","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"ZenHive","product":"mpp","packageName":"mpp","packageURL":"pkg:hex/mpp","defaultStatus":"unaffected","versions":[{"version":"0.2.0","status":"affected","lessThan":"0.6.1","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Methods.Tempo'"],"programFiles":["lib/mpp/methods/tempo.ex"],"programRoutines":[{"name":"'Elixir.MPP.Methods.Tempo':verify/2"}],"repo":"https://github.com/ZenHive/mpp"},{"vendor":"ZenHive","product":"mpp","packageName":"zenhive/mpp","packageURL":"pkg:github/zenhive/mpp","defaultStatus":"unaffected","versions":[{"version":"f8904666061fbab695874856d8fcd02c471dfe1b","status":"affected","lessThan":"46c5b0e1311da7d92190dc7d9ea89027a1d365e9","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"modules":["'Elixir.MPP.Methods.Tempo'"],"programFiles":["lib/mpp/methods/tempo.ex"],"programRoutines":[{"name":"'Elixir.MPP.Methods.Tempo':verify/2"}],"repo":"https://github.com/ZenHive/mpp"}],"references":[{"url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-w8j7-7qc3-5f24","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-73829.html","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-73829","tags":["related"]},{"url":"https://github.com/ZenHive/mpp/commit/46c5b0e1311da7d92190dc7d9ea89027a1d365e9","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":6.3,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-367","description":"CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-08-19T17:19:43.696Z"},"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>The race is only reachable when <code>MPP.Methods.Tempo</code> is configured with a dedup store (<code>\"store\"</code> in <code>method_config</code>). The default is <code>nil</code>, which runs the library statelessly and provides no application-level replay protection at all, a documented property rather than part of this issue.</p>"},{"base64":false,"type":"text/markdown","value":"The 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."}],"value":"The 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."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*","versionEndExcluding":"0.6.1","versionStartIncluding":"0.2.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"analyst","value":"Jonatan Männchen / EEF"},{"lang":"en","type":"finder","value":"E.FU"},{"lang":"en","type":"remediation developer","value":"E.FU"}],"datePublic":"2026-06-29T00:00:00.000Z","impacts":[{"capecId":"CAPEC-29","descriptions":[{"lang":"en","value":"CAPEC-29 Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions"}]}],"source":{"discovery":"EXTERNAL"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-19T18:55:14.304500Z","id":"CVE-2026-73829","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-19T18:58:33.322Z"}}]}}}