eef-cve-2026-89420

{
  "affected": [
    {
      "database_specific": {
        "source": "https://cna.erlef.org/osv/EEF-CVE-2026-89420.json"
      },
      "package": {
        "ecosystem": "Hex",
        "name": "mpp",
        "purl": "pkg:hex/mpp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.14.0"
            },
            {
              "fixed": "0.16.2"
            }
          ],
          "type": "SEMVER"
        }
      ],
      "versions": [
        "0.14.0",
        "0.15.0",
        "0.16.0",
        "0.16.1"
      ]
    },
    {
      "database_specific": {
        "source": "https://cna.erlef.org/osv/EEF-CVE-2026-89420.json"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "82df569c898be1137189e3648e1edb4af6363651"
            },
            {
              "fixed": "7270edc1dcfb58250cc5ee812876609206564165"
            }
          ],
          "repo": "https://github.com/ZenHive/mpp",
          "type": "GIT"
        }
      ],
      "versions": [
        "v0.16.1",
        "v0.16.0",
        "v0.15.0",
        "v0.14.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-89420",
    "GHSA-8c63-r789-xrrf"
  ],
  "credits": [
    {
      "name": "E.FU",
      "type": "FINDER"
    },
    {
      "name": "E.FU",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Jonatan Männchen / EEF",
      "type": "COORDINATOR"
    }
  ],
  "database_specific": {
    "capec_ids": [
      "CAPEC-212"
    ],
    "cpe_ids": [
      "cpe:2.3:a:ZenHive:mpp:*:*:*:*:*:*:*:*"
    ],
    "cwe_ids": [
      "CWE-1284"
    ]
  },
  "details": "## Summary\n\nImproper 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\n`MPP.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.\n\n## Impact\n\nA client that has opened and funded a payment channel once can re-present the same signed voucher indefinitely and receive paid resources without any further charge. Operators running mpp as paid-API middleware lose revenue in proportion to how much the client consumes, with nothing in the channel state recording the usage.",
  "id": "EEF-CVE-2026-89420",
  "modified": "2026-09-22T11:40:55.031451599Z",
  "published": "2026-09-22T11:16:29.573Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/ZenHive/mpp/security/advisories/GHSA-8c63-r789-xrrf"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-89420.html"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ZenHive/mpp/commit/82df569c898be1137189e3648e1edb4af6363651"
    },
    {
      "type": "FIX",
      "url": "https://github.com/ZenHive/mpp/commit/7270edc1dcfb58250cc5ee812876609206564165"
    },
    {
      "type": "PACKAGE",
      "url": "https://hex.pm/packages/mpp"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Session voucher adding no new funds is accepted without a charge in mpp, serving paid resources for free"
}