GHSA-MWV9-GP5H-FRR4

Vulnerability from github – Published: 2026-03-12 16:38 – Updated: 2026-05-14 21:28
VLAI
Summary
Sveltejs devalue's `devalue.parse` and `devalue.unflatten` emit objects with `__proto__` own properties
Details

In some circumstances, devalue.parse and devalue.unflatten could emit objects with __proto__ own properties. This in and of itself is not a security vulnerability (and is possible with, for example, JSON.parse as well), but it can result in prototype injection if downstream code handles it incorrectly:

const result = devalue.parse(/* input creating an object with a __proto__ property */);
const target = {};
Object.assign(target, result); // target's prototype is now polluted
Severity
2.7 (Low)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "devalue"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "5.6.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-12T16:38:15Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "In some circumstances, `devalue.parse` and `devalue.unflatten` could emit objects with `__proto__` own properties. This in and of itself is not a security vulnerability (and is possible with, for example, `JSON.parse` as well), but it can result in prototype injection if _downstream_ code handles it incorrectly:\n\n```ts\nconst result = devalue.parse(/* input creating an object with a __proto__ property */);\nconst target = {};\nObject.assign(target, result); // target\u0027s prototype is now polluted\n```",
  "id": "GHSA-mwv9-gp5h-frr4",
  "modified": "2026-05-14T21:28:15Z",
  "published": "2026-03-12T16:38:15Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sveltejs/devalue/security/advisories/GHSA-mwv9-gp5h-frr4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sveltejs/devalue"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sveltejs/devalue/releases/tag/v5.6.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Sveltejs devalue\u0027s `devalue.parse` and `devalue.unflatten` emit objects with `__proto__` own properties"
}


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