{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "1.1.2"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "680a5ebe1194edda16fa93baaa56ff14fe0e3d7f"
            },
            {
              "fixed": "bea35426afae09a9150ff0100045b64d40101a30"
            }
          ],
          "repo": "https://github.com/joaonuno/flat-to-nested-js",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-hp36-v28f-w3r4"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-1321",
      "CWE-915"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55091.json"
  },
  "details": "flat-to-nested converts a hierarchy from a flat representation to a nested representation. Prior to 1.1.2, FlatToNested.prototype.convert in index.js uses attacker-influenced id and parent record fields directly as keys in the plain temp and pendingChildOf objects. When parent or id is __proto__, temp[parent] can resolve to Object.prototype, and initPush() can write attacker-controlled data to the global children prototype property while existing prototype methods remain intact. Any application that passes attacker-influenced flat records to convert() can therefore expose unrelated objects to polluted inherited state, causing application-logic corruption or denial of service and potentially enabling greater impact when a downstream prototype-pollution gadget is present. The constructor and prototype strings are also unsafe inherited-key values in the same lookup design. This issue is fixed in version 1.1.2.",
  "id": "CVE-2026-55091",
  "modified": "2026-09-16T03:30:42.642169880Z",
  "published": "2026-09-14T17:26:38.877Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55091.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55091"
    },
    {
      "type": "FIX",
      "url": "https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "flat-to-nested: Prototype pollution in flat-to-nested convert() via __proto__ parent/id key"
}