toml-node: Prototype pollution: parsing a TOML document can write to Object.prototype

{
  "id": "7dd442df13b6a276b28a2aa0c9be86848eb1957202436083db001a199ba1f26a",
  "url": "https://osv.dev/vulnerability/GHSA-h895-cgqg-jf52",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "toml-node: Prototype pollution: parsing a TOML document can write to Object.prototype",
    "summary": "### Summary CVE-2026-63376 described prototype pollution through __proto__ key-path desynchronization and was fixed in 4.1.2 by rewriting the path bookkeeping and adding an ownedContainers WeakSet. The desynchronization is still reachable, spelled with a quote character instead of a dot, and the owned-container check is not applied on the path that matters. A four-line TOML document parsed with toml.parse() writes a property onto Object.prototype, where it is visible to every object in the process — including objects produced by unrelated libraries. ### Details Three gaps compose. All line numbers are `lib/compiler.js` in 5.0.0. **1. The path-key encoding is ambiguous.** `quoteDottedString()` quotes a segment only when it contains a `.`, and never escapes a `\"` inside the segment: ```js 287: function quoteDottedString(str) { 288: if (str.indexOf(\".\") > -1) { 289: return \"\\\"\" + str + \"\\\"\"; 290: } else { 291: return str; 292: } 293: } ``` So the key path `['x.y']` and the key path `['\"x', 'y\"']` both render as the string `\"x.y\"`. This is the same desynchronization CVE-2026-63376 named, with a quote in place of the dot. **2. A table-array header can clear another key's guard.** `addTableArray()` walks `assignedPaths` / `valueAssignments` with `isSameOrSubPath()` over those ambiguous strings, so a header whose rendered path collides with an unrelated key deletes that key's entry. **3. The descent in `assign()` has no owned-container check.** `deepRef()` applies `isOwnedContainer(",
    "evidence": "osv:GHSA-h895-cgqg-jf52",
    "products": [
      {
        "name": {
          "value": "toml",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.0.1",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "GHSA-h895-cgqg-jf52",
      "aliases": [
        "CVE-2026-114142",
        "GHSA-h895-cgqg-jf52"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "5.0.1"
                }
              ]
            }
          ],
          "package": {
            "name": "toml",
            "purl": "pkg:npm/toml",
            "ecosystem": "npm"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-h895-cgqg-jf52/GHSA-h895-cgqg-jf52.json",
            "last_known_affected_version_range": "<= 5.0.0"
          }
        }
      ],
      "modified": "2026-10-26T14:45:05.681971920Z",
      "provider": "osv",
      "references": [
        "https://github.com/BinaryMuse/toml-node/security/advisories/GHSA-h895-cgqg-jf52",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-114142",
        "https://github.com/BinaryMuse/toml-node/commit/609c873fffea0a27ebe5b4dd098eed2b3daf3606",
        "https://github.com/BinaryMuse/toml-node",
        "https://github.com/BinaryMuse/toml-node/releases/tag/v5.0.1"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1321"
        ],
        "severity": "HIGH",
        "github_reviewed": true,
        "nvd_published_at": "2026-10-21T21:17:56Z",
        "github_reviewed_at": "2026-10-22T16:39:55Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-114142",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 454226,
  "published_at": "2026-10-22T16:39:55+00:00"
}