{"id":"EEF-CVE-2026-87119","summary":"mpp Tempo subscription key authorization is not bound to the issuing challenge, allowing a captured activation credential to be replayed","details":"## Summary\n\nAuthentication 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.\n\n## Impact\n\nAn 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.\n\n## Configurations\n\nOnly 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.","aliases":["CVE-2026-87119","GHSA-p9fv-9w58-95x2"],"modified":"2026-09-22T11:40:55.168831655Z","published":"2026-09-22T11:16:56.232Z","database_specific":{"capec_ids":["CAPEC-60"],"cpe_ids":["cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"],"cwe_ids":["CWE-294"]},"references":[{"type":"ADVISORY","url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-p9fv-9w58-95x2"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-87119.html"},{"type":"WEB","url":"https://github.com/ZenHive/mpp/commit/db464dfa9a86ccda58f0827101f6da6bd8aafa78"},{"type":"FIX","url":"https://github.com/ZenHive/mpp/commit/4b6eaec02af0e8485cfb4ff68f467d075ed5dd6f"},{"type":"PACKAGE","url":"https://hex.pm/packages/mpp"}],"affected":[{"package":{"name":"mpp","ecosystem":"Hex","purl":"pkg:hex/mpp"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.14.0"},{"fixed":"0.16.2"}]}],"versions":["0.14.0","0.15.0","0.16.0","0.16.1"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-87119.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/ZenHive/mpp","events":[{"introduced":"db464dfa9a86ccda58f0827101f6da6bd8aafa78"},{"fixed":"4b6eaec02af0e8485cfb4ff68f467d075ed5dd6f"}]}],"versions":["v0.16.1","v0.16.0","v0.15.0","v0.14.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-87119.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}],"credits":[{"name":"E.FU","type":"FINDER"},{"name":"E.FU","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen / EEF","type":"COORDINATOR"}]}