{"cve":"CVE-2026-89420","nvd":{"published":"2026-09-22T12:17:14.370","modified":"2026-09-22T19:09:32.273","status":"Deferred","description":"Improper Validation of Specified Quantity in Input in ZenHive mpp allows a client holding an open payment channel to obtain paid resources without being charged.\n\nMPP.Session.Actions.accept_voucher/3 in lib/mpp/session/actions.ex treats a voucher whose cumulativeAmount equals the channel's already-accepted cumulative amount as an idempotent success, returning the channel unchanged without calling maybe_spend/2. The credential verifies, the protected resource is served, and spent and units stay where they were. Because the server issues a fresh challenge per request and the credential replay store keys on challenge id and payload, the same signed voucher can be re-presented under every new challenge, so one paid voucher yields an unbounded number of paid units. The path is reachable from any method built on MPP.Session.Method through the Plug, MCP, JSON-RPC and WebSocket transports.\n\nThis issue affects mpp: from 0.14.0 before 0.16.2.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N","score":7.1},"cvss_v3":null,"cwes":["CWE-1284"],"references":["https://cna.erlef.org/cves/CVE-2026-89420.html","https://github.com/ZenHive/mpp/commit/7270edc1dcfb58250cc5ee812876609206564165","https://github.com/ZenHive/mpp/commit/82df569c898be1137189e3648e1edb4af6363651","https://github.com/ZenHive/mpp/security/advisories/GHSA-8c63-r789-xrrf","https://osv.dev/vulnerability/EEF-CVE-2026-89420"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:56:02.509636177+00:00"},"epss":{"cve":"CVE-2026-89420","score":0.00409,"percentile":0.35149,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}