Only deployments offering Tempo subscriptions are affected, which requires subscription_access_key_private_key in the Tempo method_config. Exploitation further requires the attacker to have obtained a payer's signed activation credential, in transit over a hop that is not TLS-protected or at rest in a log, an intermediary, or a client retry buffer.
Authentication Bypass by Capture-replay in ZenHive mpp allows an attacker holding a captured subscription activation credential to charge the payer repeatedly.
\nThe payer signs a Tempo KeyAuthorization over the chain id, key type, key id, expiry, limits and scopes only, with nothing tying it to the challenge that prompted it. MPP.Methods.Tempo.KeyAuthorization.verify/3 in lib/mpp/methods/tempo/key_authorization.ex pins each of those signed fields against the subscription request, and the access key it pins is a static per-endpoint server key, so one signed authorization verifies against every challenge the server issues for the same subscription terms. MPP.Methods.Tempo.Subscription.activate/4 deduplicates activations by challenge id, so presenting the captured credential under a fresh challenge produces a different dedup key, claim_activation succeeds, and the subscription transaction is built and broadcast again. Each replay charges the payer's wallet a new first-period settlement and re-authorizes the server key, bounded only by the subscription expiry and the chain's own semantics for re-installing an existing key.
This issue affects mpp: from 0.14.0 before 0.16.2.
"},{"base64":false,"type":"text/markdown","value":"Authentication Bypass by Capture-replay in ZenHive mpp allows an attacker holding a captured subscription activation credential to charge the payer repeatedly.\n\nThe payer signs a Tempo `KeyAuthorization` over the chain id, key type, key id, expiry, limits and scopes only, with nothing tying it to the challenge that prompted it. `MPP.Methods.Tempo.KeyAuthorization.verify/3` in `lib/mpp/methods/tempo/key_authorization.ex` pins each of those signed fields against the subscription request, and the access key it pins is a static per-endpoint server key, so one signed authorization verifies against every challenge the server issues for the same subscription terms. `MPP.Methods.Tempo.Subscription.activate/4` deduplicates activations by challenge id, so presenting the captured credential under a fresh challenge produces a different dedup key, `claim_activation` succeeds, and the subscription transaction is built and broadcast again. Each replay charges the payer's wallet a new first-period settlement and re-authorizes the server key, bounded only by the subscription expiry and the chain's own semantics for re-installing an existing key.\n\nThis issue affects mpp: from 0.14.0 before 0.16.2."}],"value":"Authentication Bypass by Capture-replay in ZenHive mpp allows an attacker holding a captured subscription activation credential to charge the payer repeatedly.\n\nThe payer signs a Tempo KeyAuthorization over the chain id, key type, key id, expiry, limits and scopes only, with nothing tying it to the challenge that prompted it. MPP.Methods.Tempo.KeyAuthorization.verify/3 in lib/mpp/methods/tempo/key_authorization.ex pins each of those signed fields against the subscription request, and the access key it pins is a static per-endpoint server key, so one signed authorization verifies against every challenge the server issues for the same subscription terms. MPP.Methods.Tempo.Subscription.activate/4 deduplicates activations by challenge id, so presenting the captured credential under a fresh challenge produces a different dedup key, claim_activation succeeds, and the subscription transaction is built and broadcast again. Each replay charges the payer's wallet a new first-period settlement and re-authorizes the server key, bounded only by the subscription expiry and the chain's own semantics for re-installing an existing key.\n\nThis issue affects mpp: from 0.14.0 before 0.16.2."}],"impacts":[{"capecId":"CAPEC-60","descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"An attacker who obtains a payer's subscription activation credential (from a non-TLS hop, a log, a compromised intermediary, or the client's own retry buffer) can present it under fresh challenges to settle repeated first-period charges against that payer's wallet and re-authorize the server's access key. The payer bears the on-chain cost, limited only by the per-period subscription limit and the subscription expiry.
"},{"base64":false,"type":"text/markdown","value":"An attacker who obtains a payer's subscription activation credential (from a non-TLS hop, a log, a compromised intermediary, or the client's own retry buffer) can present it under fresh challenges to settle repeated first-period charges against that payer's wallet and re-authorize the server's access key. The payer bears the on-chain cost, limited only by the per-period subscription limit and the subscription expiry."}],"value":"An attacker who obtains a payer's subscription activation credential (from a non-TLS hop, a log, a compromised intermediary, or the client's own retry buffer) can present it under fresh challenges to settle repeated first-period charges against that payer's wallet and re-authorize the server's access key. The payer bears the on-chain cost, limited only by the per-period subscription limit and the subscription expiry."}]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"HIGH","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":8.2,"baseSeverity":"HIGH","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-294","description":"CWE-294 Authentication Bypass by Capture-replay","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-09-22T11:16:56.232Z","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","shortName":"EEF"},"references":[{"name":"GitHub Advisory","tags":["related","vendor-advisory"],"url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-p9fv-9w58-95x2"},{"name":"EEF CNA record for CVE-2026-87119","tags":["related"],"url":"https://cna.erlef.org/cves/CVE-2026-87119.html"},{"name":"OSV record EEF-CVE-2026-87119","tags":["related"],"url":"https://osv.dev/vulnerability/EEF-CVE-2026-87119"},{"name":"Introducing commit db464df in ZenHive/mpp","tags":["related"],"url":"https://github.com/ZenHive/mpp/commit/db464dfa9a86ccda58f0827101f6da6bd8aafa78"},{"name":"Fix commit 4b6eaec in ZenHive/mpp","tags":["patch"],"url":"https://github.com/ZenHive/mpp/commit/4b6eaec02af0e8485cfb4ff68f467d075ed5dd6f"}],"source":{"discovery":"INTERNAL"},"title":"mpp Tempo subscription key authorization is not bound to the issuing challenge, allowing a captured activation credential to be replayed"}},"cveMetadata":{"assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","assignerShortName":"EEF","cveId":"CVE-2026-87119","datePublished":"2026-09-22T11:16:56.232Z","dateReserved":"2026-09-11T18:00:02.032Z","dateUpdated":"2026-09-22T11:16:56.232Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"}