mpp writes Payment-Receipt and Cache-Control before the wrapped application runs, letting a consumer's own Cache-Control expose paid responses to shared caches

{
  "id": "62eecec35b8b1179e37414d8a6c44d94b7a56cd982a1d52578fdc8eea1154411",
  "url": "https://osv.dev/vulnerability/CVE-2026-89186",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mpp writes Payment-Receipt and Cache-Control before the wrapped application runs, letting a consumer's own Cache-Control expose paid responses to shared caches",
    "summary": "Use of Cache Containing Sensitive Information in ZenHive mpp allows a shared HTTP cache to store a paid response and serve it to clients that never paid. MPP.Plug.verify_credential in lib/mpp/plug.ex sets payment-receipt and cache-control: private on the connection before the wrapped application runs, and registers no register_before_send/2 callback. Plug.Conn.put_resp_header/3 replaces an existing header, so a mounting application that sets its own cache-control on the paid resource (for example public, max-age=3600) silently overrides the private the library relies on, and a CDN or reverse proxy can then store the paid 200 together with its Payment-Receipt and serve both to unpaid clients. The library-level guarantee is therefore defeatable by the application it protects. For the same reason a downstream non-2xx response still carried Payment-Receipt, issuing a receipt for a response that delivered no resource. This issue affects mpp: from 0.1.0 before 0.16.2.",
    "evidence": "osv:CVE-2026-89186",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-89186",
      "aliases": [
        "CVE-2026-89186",
        "EEF-CVE-2026-89186",
        "GHSA-82qh-vrvm-gqvc"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/zenhive/mpp",
              "type": "GIT",
              "events": [
                {
                  "introduced": "8e43e7285931741e2b9aecf90c8439bb84ca8e4c"
                },
                {
                  "fixed": "3b7e43abf60fa30c40985e4043965ec67791b4dc"
                },
                {
                  "fixed": "2d4d1d94aae7790ae0623063961adbeef171fa71"
                },
                {
                  "fixed": "2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0.1.0"
                      },
                      {
                        "fixed": "0.16.2"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "2d4d1d94aae7790ae0623063961adbeef171fa71"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.16.1",
            "v0.16.0",
            "v0.15.0",
            "v0.14.0",
            "v0.13.0",
            "v0.12.0",
            "v0.11.0",
            "v0.10.0",
            "v0.9.0",
            "v0.8.0",
            "v0.7.0",
            "v0.6.4",
            "v0.6.3",
            "v0.6.1",
            "v0.6.0",
            "v0.5.1",
            "v0.4.0",
            "v0.3.0",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89186.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:39.308196095Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-89186.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-89186",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89186.json",
        "https://github.com/ZenHive/mpp/security/advisories/GHSA-82qh-vrvm-gqvc",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89186",
        "https://github.com/ZenHive/mpp/commit/2d4d1d94aae7790ae0623063961adbeef171fa71",
        "https://github.com/ZenHive/mpp/commit/2fd91a5ecbd0b0ad2a4ac202b79659e8126dbc0b",
        "https://github.com/ZenHive/mpp"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-524"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89186.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-89186",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 506692,
  "published_at": "2026-09-16T08:24:15.058+00:00"
}