{"id":"CVE-2026-55091","revision":null,"records":[{"revision":"fd8643a77035425b88b73c2262afd5cf","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-55091","aliases":[],"title":"flat-to-nested: Prototype pollution in flat-to-nested convert() via __proto__ parent/id key","description":"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.","state":0,"publishedAt":"2026-09-14T17:26:38.877+00:00","modifiedAt":"2026-09-14T20:05:59.07+00:00","affected":[{"ecosystem":"Vendor product","name":"flat-to-nested-js","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"joaonuno\",\n                    \"product\": \"flat-to-nested-js\",\n                    \"versions\": [\n                        {\n                            \"version\": \"< 1.1.2\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5,"severity":"HIGH"}],"references":["https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4","https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f","https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-55091","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-55091","identifiers":["CVE-2026-55091"]},"retained":false,"historicalAffected":[]},{"revision":"707f805747bc43129940eb7c01ed296b","observedAt":"2026-11-11T16:11:16.59+00:00","statement":{"source":"euvd","id":"EUVD-2026-77691","aliases":["CVE-2026-55091","GHSA-hp36-v28f-w3r4"],"title":"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 an…","description":"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.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5,"severity":null}],"references":["https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4","https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f","https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-77691","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Sep 14, 2026, 5:26:38 PM","dateUpdated":"Sep 14, 2026, 8:05:59 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-77691","identifiers":["EUVD-2026-77691","CVE-2026-55091","GHSA-hp36-v28f-w3r4"]},"retained":false,"historicalAffected":[]},{"revision":"6ecd291ad74a43c296d6c7838b76b11b","observedAt":"2026-10-25T13:17:34.255+00:00","statement":{"source":"nvd","id":"CVE-2026-55091","aliases":[],"title":"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 an…","description":"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.","state":0,"publishedAt":"2026-09-14T18:17:54.79+00:00","modifiedAt":"2026-09-30T17:51:56.193+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · security-advisories@github.com · Secondary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5,"severity":"HIGH"}],"references":["https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f","https://github.com/joaonuno/flat-to-nested-js/releases/tag/v1.1.2","https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-55091","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Deferred","weaknesses":["CWE-915","CWE-1321"],"productCriteria":[],"sourceDates":{"published":"2026-09-14T18:17:54.790","lastModified":"2026-09-30T17:51:56.193"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-55091","identifiers":["CVE-2026-55091"]},"retained":false,"historicalAffected":[]},{"revision":"841f1c924e37429daad13ba6a0ab2e88","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-hp36-v28f-w3r4","aliases":["CVE-2026-55091"],"title":"flat-to-nested: Prototype pollution in flat-to-nested convert() via __proto__ parent/id key","description":"### Summary\n  `convert()` builds the nested tree by using each flat record's `id` and `parent` field values directly as object keys, with no guard against `__proto__` / `constructor` / `prototype`. A record whose `parent` is the string `\"__proto__\"` makes `temp[parent]` resolve to `Object.prototype`, and the following `initPush(...)` writes attacker-controlled data onto the global prototype. Any application that passes attacker-influenced records to `convert()` is affected, and the base prototype methods stay intact so the pollution is stealthy.\n\n  ### Details\n  In `index.js`, `convert()` (`FlatToNested.prototype.convert`):\n\n  - `temp = {}` (line 45) and `pendingChildOf = {}` (line 46) are plain objects, so they inherit from `Object.prototype`.\n  - For each record, `parent = flatEl[this.config.parent]` (line 51) is taken verbatim from input.\n  - Line 57: `if (temp[parent] !== undefined)` — when `parent === \"__proto__\"`, `temp[\"__proto__\"]` resolves via the prototype chain to `Object.prototype`, which is `!== undefined`, so the\n  branch is taken.\n  - Line 59: `initPush(this.config.children, temp[parent], flatEl)` → effectively `initPush(\"children\", Object.prototype, flatEl)`.\n  - `initPush` (lines 4-9): `Object.prototype[\"children\"] = []` then `Object.prototype[\"children\"].push(flatEl)` — **attacker-controlled data is written onto the global `Object.prototype`.**\n\n  There is no sanitization of `id` / `parent` anywhere; they flow straight into `temp[id]`, `temp[parent]`, and `pendingChildOf[parent]` as dynamic keys.\n\n  ### PoC\n  ```js\n  const FlatToNested = require('flat-to-nested');\n\n  new FlatToNested().convert([\n    { id: 1, parent: '__proto__', polluted: 'PWNED' }\n  ]);\n\n  console.log(({}).children); // => [ { id: 1, polluted: 'PWNED' } ]\n  A freshly-created, unrelated object {} now carries an attacker-controlled children property. ({}).toString === Object.prototype.toString remains true, so existing methods are untouched (stealthy). If the consumer configures a custom children key, that arbitrary prototype property is polluted instead.\n ```\n \n  ### Impact\n\n  Prototype pollution (CWE-1321). Any service that builds a tree from attacker-influenced flat records (the package's core purpose — e.g. records derived from a DB/REST/user input) can have Object.prototype polluted. Consequences range from application-logic corruption and denial of service to serving as a gadget toward privilege escalation or RCE depending on downstream sinks. No special privileges or user interaction required; the malicious value is ordinary input data.\n\n  ### Suggested fix\n\n  Use prototype-less lookup tables so inherited keys like __proto__ cannot be reached:\n  var temp = Object.create(null);\n  var pendingChildOf = Object.create(null);\n  (Optionally also reject id/parent values equal to __proto__, constructor, or prototype.) Verified: with Object.create(null) for both temp and pendingChildOf, the PoC no longer pollutes Object.prototype and normal nesting output is unchanged. A patch with a regression test is ready.","state":0,"publishedAt":"2026-06-19T20:47:52+00:00","modifiedAt":"2026-06-19T21:11:28.86403+00:00","affected":[{"ecosystem":"npm","name":"flat-to-nested","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"1.1.2"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"HIGH"}],"references":["https://github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v28f-w3r4","https://github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baaa56ff14fe0e3d7f","https://github.com/joaonuno/flat-to-nested-js"],"sourceUrl":"https://github.com/advisories/GHSA-hp36-v28f-w3r4","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-hp36-v28f-w3r4","identifiers":["GHSA-hp36-v28f-w3r4","CVE-2026-55091"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. Missing entries do not establish absence of exploitation.","generation":"2026-11-12T02:56:45.8822264+00:00","complete":true,"records":1779,"lastAttemptAt":"2026-11-12T02:56:45.8822264+00:00","lastSuccessAt":"2026-11-12T02:56:46.0427292+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:46.0427301+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"cve-program","scope":"Official CVE Program baseline and cumulative hourly delta; all vendors, published and rejected records","generation":"cve-64752486c567b55b31fb0d7225f5222bcd0019564ac0ac5f0649e242c7b19299-c8f0a5eb97b437649f83f6fe632ec849fcb249052407d33e475e82c88b318dfb","complete":true,"records":424535,"lastAttemptAt":"2026-11-12T02:56:45.3610802+00:00","lastSuccessAt":"2026-11-12T02:56:45.341976+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:45.3610802+00:00","snapshotPublishedAt":"2026-11-12T02:25:26+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"euvd","scope":"Rolling EUVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global EUVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-3bce114846604d92838a2dc302341627","complete":false,"records":13760,"lastAttemptAt":"2026-11-12T03:06:53.8778262+00:00","lastSuccessAt":"2026-11-12T03:06:52.8+00:00","error":"754 identifier lookups failed; latest failures include AccessDenied (HTTP 403). Other identifiers were checked independently.","lastVerifiedAt":"2026-11-12T03:06:52.8+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13040,"expectedIdentifiers":13813,"failedIdentifiers":754},{"source":"first-epss:nuget","scope":"FIRST EPSS for explicit CVE aliases in the collected public NuGet archive. Not a global EPSS backfill.","generation":"2026-11-12T02:56:45.8822264+00:00","complete":true,"records":1097,"lastAttemptAt":"2026-11-12T02:56:45.8822264+00:00","lastSuccessAt":"2026-11-12T02:56:46.0434469+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:46.0434471+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"nvd","scope":"Rolling NVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global NVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-729a419ccc5f41d8a3330c7c6e8b6a5e","complete":true,"records":13760,"lastAttemptAt":"2026-11-12T02:57:11.7691852+00:00","lastSuccessAt":"2026-11-12T02:57:11.766+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:57:11.766+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13813,"expectedIdentifiers":13813,"failedIdentifiers":0},{"source":"osv:Go","scope":"Complete OSV Go ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"go-3562b6c78fd1bd0f0b55daf66a0926ae24f65e462df7f6d928caad458fc696bf","complete":true,"records":9947,"lastAttemptAt":"2026-11-12T02:56:45.7363501+00:00","lastSuccessAt":"2026-11-11T04:27:43.6877707+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:45.7363501+00:00","snapshotPublishedAt":"2026-11-11T03:32:46+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:NuGet","scope":"Complete OSV NuGet ecosystem archive, including GitHub Advisory Database records; NuGet version matching only","generation":"nuget-456002455e0ab94bb92c95476d4e6d175c104cd594749982afd96c893728ecbc","complete":true,"records":2010,"lastAttemptAt":"2026-11-12T02:56:45.5271491+00:00","lastSuccessAt":"2026-11-11T02:36:58.1276999+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:45.5271491+00:00","snapshotPublishedAt":"2026-11-11T01:17:51+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:crates.io","scope":"Complete OSV crates.io ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"crates.io-baa8362b4daf9e5f39d5563775a55935e7b442c0735d33274a921579ce4a0d66","complete":true,"records":3093,"lastAttemptAt":"2026-11-12T02:56:45.8443473+00:00","lastSuccessAt":"2026-11-11T13:00:02.5446881+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:45.8443473+00:00","snapshotPublishedAt":"2026-11-11T12:47:47+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:npm","scope":"Complete OSV npm ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"npm-685fe7fb2b690656c910a1ea42a9d294e8353311ac8ecfa691a9b0ff1b328804","complete":true,"records":231695,"lastAttemptAt":"2026-11-12T02:56:45.6384803+00:00","lastSuccessAt":"2026-11-11T21:58:47.7265713+00:00","error":null,"lastVerifiedAt":"2026-11-12T02:56:45.6384803+00:00","snapshotPublishedAt":"2026-11-11T21:48:35+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null}]}