flatted: Prototype Pollution via parse()

{
  "id": "5d01301ca198a91181fe833143b7dc5d50f78168d4249c83274c50062fd59c19",
  "url": "https://osv.dev/vulnerability/CVE-2026-33228",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "flatted: Prototype Pollution via parse()",
    "summary": "flatted is a circular JSON parser. Prior to version 3.4.2, the parse() function in flatted can use attacker-controlled string values from the parsed JSON as direct array index keys, without validating that they are numeric. Since the internal input buffer is a JavaScript Array, accessing it with the key \"__proto__\" returns Array.prototype via the inherited getter. This object is then treated as a legitimate parsed value and assigned as a property of the output object, effectively leaking a live reference to Array.prototype to the consumer. Any code that subsequently writes to that property will pollute the global prototype. This issue has been patched in version 3.4.2.",
    "evidence": "osv:CVE-2026-33228",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-33228",
      "aliases": [
        "CVE-2026-33228",
        "GHSA-rf6f-7fwh-wjgh"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/webreflection/flatted",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "3bf09091c3562e17a0647bc06710dd6097079cf7"
                },
                {
                  "fixed": "885ddcc33cf9657caf38c57c7be45ae1c5272802"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:webreflection:flatted:*:*:*:*:*:node.js:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "3.4.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "885ddcc33cf9657caf38c57c7be45ae1c5272802"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "3bf09091c3562e17a0647bc06710dd6097079cf7"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v3.4.2"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.4.1",
            "v3.4.0",
            "v3.3.4",
            "v3.3.3",
            "v3.3.2",
            "v3.3.1",
            "v3.3.0",
            "v3.2.13",
            "v3.2.12",
            "v3.2.11",
            "v3.2.10",
            "v3.2.8",
            "v3.2.7",
            "v3.2.6",
            "v3.2.5",
            "v3.2.4",
            "v3.2.3",
            "v3.2.2",
            "v3.2.1",
            "v3.2.0",
            "v3.1.1",
            "v3.0.5",
            "v3.0.4",
            "v3.0.3",
            "v3.0.2",
            "v3.0.1",
            "v3.0.0",
            "v2.0.2",
            "v2.0.1",
            "v2.0.0",
            "v1.0.3",
            "v1.0.2",
            "v1.0.1",
            "v1.0.0",
            "v0.2.3",
            "v0.2.2",
            "v0.2.1",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-33228.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.594448501Z",
      "provider": "osv",
      "references": [
        "https://github.com/WebReflection/flatted/releases/tag/v3.4.2",
        "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33228.json",
        "https://access.redhat.com/errata/RHSA-2026:13826",
        "https://access.redhat.com/errata/RHSA-2026:34342",
        "https://access.redhat.com/errata/RHSA-2026:9742",
        "https://access.redhat.com/security/cve/CVE-2026-33228",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33228.json",
        "https://github.com/WebReflection/flatted/security/advisories/GHSA-rf6f-7fwh-wjgh",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-33228",
        "https://bugzilla.redhat.com/show_bug.cgi?id=2449872",
        "https://github.com/WebReflection/flatted/commit/885ddcc33cf9657caf38c57c7be45ae1c5272802"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1321"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33228.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-33228",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489924,
  "published_at": "2026-03-20T23:06:48.485+00:00"
}