{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-88255", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-09-11T18:30:01.336Z", "datePublished": "2026-09-16T08:24:40.446Z", "dateUpdated": "2026-09-16T08:24:40.446Z"}, "containers": {"cna": {"affected": [{"collectionURL": "https://repo.hex.pm", "cpes": ["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.MPP.Methods.Tempo'"], "packageName": "mpp", "packageURL": "pkg:hex/mpp", "product": "mpp", "programFiles": ["lib/mpp/methods/tempo.ex"], "programRoutines": [{"name": "'Elixir.MPP.Methods.Tempo':verify/2"}], "repo": "https://github.com/ZenHive/mpp", "vendor": "ZenHive", "versions": [{"lessThan": "0.16.2", "status": "affected", "version": "0.2.0", "versionType": "semver"}]}, {"collectionURL": "https://github.com", "cpes": ["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"], "defaultStatus": "unaffected", "modules": ["'Elixir.MPP.Methods.Tempo'"], "packageName": "zenhive/mpp", "packageURL": "pkg:github/zenhive/mpp", "product": "mpp", "programFiles": ["lib/mpp/methods/tempo.ex"], "programRoutines": [{"name": "'Elixir.MPP.Methods.Tempo':verify/2"}], "repo": "https://github.com/ZenHive/mpp", "vendor": "ZenHive", "versions": [{"lessThan": "e12bd4a1cea2e97c2a01fc059c48e5594a7b4a43", "status": "affected", "version": "f8904666061fbab695874856d8fcd02c471dfe1b", "versionType": "git"}]}], "configurations": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Reachable when <code>MPP.Methods.Tempo</code> broadcasts a <code>type=\"transaction\"</code> credential with a dedup store in place. From mpp 0.7.0 the dedup store is on by default (the app-started <code>MPP.Tempo.ConCacheStore</code>; opt out with <code>store: false</code>), so every default Tempo deployment from 0.7.0 before 0.16.2 is affected. Before 0.7.0 the default store was <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; those versions are affected only where a <code>\"store\"</code> was configured explicitly in <code>method_config</code>.</p>"}, {"base64": false, "type": "text/markdown", "value": "Reachable when `MPP.Methods.Tempo` broadcasts a `type=\"transaction\"` credential with a dedup store in place. From mpp 0.7.0 the dedup store is on by default (the app-started `MPP.Tempo.ConCacheStore`; opt out with `store: false`), so every default Tempo deployment from 0.7.0 before 0.16.2 is affected. Before 0.7.0 the default store was `nil`, which runs the library statelessly and provides no application-level replay protection at all, a documented property rather than part of this issue; those versions are affected only where a `\"store\"` was configured explicitly in `method_config`."}], "value": "Reachable when MPP.Methods.Tempo broadcasts a type=\"transaction\" credential with a dedup store in place. From mpp 0.7.0 the dedup store is on by default (the app-started MPP.Tempo.ConCacheStore; opt out with store: false), so every default Tempo deployment from 0.7.0 before 0.16.2 is affected. Before 0.7.0 the default store was nil, which runs the library statelessly and provides no application-level replay protection at all, a documented property rather than part of this issue; those versions are affected only where a \"store\" was configured explicitly in method_config."}], "cpeApplicability": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*", "versionEndExcluding": "0.16.2", "versionStartIncluding": "0.2.0", "vulnerable": true}], "negate": false, "operator": "OR"}], "operator": "AND"}], "credits": [{"lang": "en", "type": "finder", "value": "E.FU"}, {"lang": "en", "type": "remediation developer", "value": "E.FU"}, {"lang": "en", "type": "coordinator", "value": "Jonatan M\u00e4nnchen / EEF"}], "dateAssigned": "2026-09-15T15:20:56.000Z", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>Improper Validation of Unsafe Equivalence in Input in ZenHive mpp allows an unauthenticated remote client to pass the Tempo duplicate-submission gate twice with one signed transaction.</p>\n<p><code>MPP.Methods.Tempo</code> reserves the pre-broadcast dedup slot on the caller-supplied hex in <code>reserve_hash_atomic/2</code>, keyed through <code>store_key/1</code> on <code>tx.raw</code> rather than on a canonical form of the transaction. The deserializer stores the caller's hex verbatim and accepts both recovery-id encodings, so one signed transaction submitted once with <code>v=27</code> and once with <code>v=0</code> yields two distinct reserve keys, and both pass the reserve and reach the broadcast path. The plug-level credential replay store is deliberately carved out for <code>tempo</code> in <code>lib/mpp/replay.ex</code>, leaving this reserve as the only gate, and the post-broadcast mark writes the canonical hash key that the raw-keyed reserve never reads.</p>\n<p>What the duplicate submission yields depends on the node: a nonce-reuse rejection fails closed, while a node that answers with the canonical hash for an already-known transaction returns a second valid <code>Payment-Receipt</code> for a single on-chain payment.</p>\n<p>This issue affects mpp: from 0.2.0 before 0.16.2.</p>"}, {"base64": false, "type": "text/markdown", "value": "Improper Validation of Unsafe Equivalence in Input in ZenHive mpp allows an unauthenticated remote client to pass the Tempo duplicate-submission gate twice with one signed transaction.\n\n`MPP.Methods.Tempo` reserves the pre-broadcast dedup slot on the caller-supplied hex in `reserve_hash_atomic/2`, keyed through `store_key/1` on `tx.raw` rather than on a canonical form of the transaction. The deserializer stores the caller's hex verbatim and accepts both recovery-id encodings, so one signed transaction submitted once with `v=27` and once with `v=0` yields two distinct reserve keys, and both pass the reserve and reach the broadcast path. The plug-level credential replay store is deliberately carved out for `tempo` in `lib/mpp/replay.ex`, leaving this reserve as the only gate, and the post-broadcast mark writes the canonical hash key that the raw-keyed reserve never reads.\n\nWhat the duplicate submission yields depends on the node: a nonce-reuse rejection fails closed, while a node that answers with the canonical hash for an already-known transaction returns a second valid `Payment-Receipt` for a single on-chain payment.\n\nThis issue affects mpp: from 0.2.0 before 0.16.2."}], "value": "Improper Validation of Unsafe Equivalence in Input in ZenHive mpp allows an unauthenticated remote client to pass the Tempo duplicate-submission gate twice with one signed transaction.\n\nMPP.Methods.Tempo reserves the pre-broadcast dedup slot on the caller-supplied hex in reserve_hash_atomic/2, keyed through store_key/1 on tx.raw rather than on a canonical form of the transaction. The deserializer stores the caller's hex verbatim and accepts both recovery-id encodings, so one signed transaction submitted once with v=27 and once with v=0 yields two distinct reserve keys, and both pass the reserve and reach the broadcast path. The plug-level credential replay store is deliberately carved out for tempo in lib/mpp/replay.ex, leaving this reserve as the only gate, and the post-broadcast mark writes the canonical hash key that the raw-keyed reserve never reads.\n\nWhat the duplicate submission yields depends on the node: a nonce-reuse rejection fails closed, while a node that answers with the canonical hash for an already-known transaction returns a second valid Payment-Receipt for a single on-chain payment.\n\nThis issue affects mpp: from 0.2.0 before 0.16.2."}], "impacts": [{"capecId": "CAPEC-267", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<p>A client re-encodes the recovery id of a transaction it has already submitted and presents it again. The duplicate passes the only duplicate-submission gate the Tempo method has, and against a node that answers with the canonical hash for an already-known transaction the client is issued a second <code>Payment-Receipt</code> for one on-chain payment.</p>"}, {"base64": false, "type": "text/markdown", "value": "A client re-encodes the recovery id of a transaction it has already submitted and presents it again. The duplicate passes the only duplicate-submission gate the Tempo method has, and against a node that answers with the canonical hash for an already-known transaction the client is issued a second `Payment-Receipt` for one on-chain payment."}], "value": "A client re-encodes the recovery id of a transaction it has already submitted and presents it again. The duplicate passes the only duplicate-submission gate the Tempo method has, and against a node that answers with the canonical hash for an already-known transaction the client is issued a second Payment-Receipt for one on-chain payment."}]}], "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-1289", "description": "CWE-1289 Improper Validation of Unsafe Equivalence in Input", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-09-16T08:24:40.446Z"}, "references": [{"name": "GitHub Advisory", "tags": ["related", "vendor-advisory"], "url": "https://github.com/ZenHive/mpp/security/advisories/GHSA-8x7x-5j8g-8hcx"}, {"name": "EEF CNA record for CVE-2026-88255", "tags": ["related"], "url": "https://cna.erlef.org/cves/CVE-2026-88255.html"}, {"name": "OSV record EEF-CVE-2026-88255", "tags": ["related"], "url": "https://osv.dev/vulnerability/EEF-CVE-2026-88255"}, {"name": "Introducing commit f890466 in ZenHive/mpp", "tags": ["related"], "url": "https://github.com/ZenHive/mpp/commit/f8904666061fbab695874856d8fcd02c471dfe1b"}, {"name": "Fix commit e12bd4a in ZenHive/mpp", "tags": ["patch"], "url": "https://github.com/ZenHive/mpp/commit/e12bd4a1cea2e97c2a01fc059c48e5594a7b4a43"}], "source": {"discovery": "INTERNAL"}, "title": "mpp Tempo keys its pre-broadcast dedup reserve on the caller-supplied transaction encoding, so a re-encoded signed transaction reserves a second slot"}}}

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