{"id":"CVE-2026-46625","aliases":["CLSA-2026-1782089812","DEBIAN-CVE-2026-46625","EUVD-2026-36154","GHSA-qjx8-664m-686j","ROOT-APP-NPM-CVE-2026-46625","UBUNTU-CVE-2026-46625"],"status":"published","title":"JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00919,"percentile":0.607,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1321","CWE-915"],"published":"2026-05-21T21:20:31Z","modified":"2026-10-28T02:30:44Z","fixes":[{"ecosystem":"npm","package":"js-cookie","fixed_in":["3.0.7"],"sources":["ghsa","osv"]},{"ecosystem":"TuxCare:npm","package":"js-cookie","fixed_in":["2.2.1-tuxcare.1"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"node-js-cookie","fixed_in":["3.0.7+~3.0.6-1"],"sources":["osv"]},{"ecosystem":"Root:npm","package":"@rootio/js-cookie","fixed_in":["2.2.1-root.io.1","3.0.5-root.io.1","3.0.5-root.io.2","2.2.1-root.io.2"],"sources":["osv"]},{"ecosystem":"Root:npm","package":"js-cookie","fixed_in":["3.0.5-aikido.2","2.2.1-aikido.2"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"3.0.5"},{"fixed":"3.0.7"}]}]},{"source":"osv","ecosystem":"TuxCare:npm","package":"js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.2.1-tuxcare.0"},{"fixed":"2.2.1-tuxcare.1"}]}],"versions":["2.2.1"]},{"source":"osv","ecosystem":"Debian:12","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.1+~3.0.0-3","3.0.7+~3.0.6-1","3.0.7+~3.0.6-2","3.0.8+~3.0.6-1"]},{"source":"osv","ecosystem":"Debian:13","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.1+~3.0.0-3","3.0.7+~3.0.6-1","3.0.7+~3.0.6-2","3.0.8+~3.0.6-1"]},{"source":"osv","ecosystem":"Debian:14","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.0.7+~3.0.6-1"}]}],"versions":["3.0.1+~3.0.0-3"]},{"source":"osv","ecosystem":"npm","package":"js-cookie","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"3.0.7"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"@rootio/js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.1-root.io.1"},{"fixed":"3.0.5-root.io.1"},{"fixed":"3.0.5-root.io.2"},{"fixed":"2.2.1-root.io.2"}]}]},{"source":"osv","ecosystem":"Root:npm","package":"js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.0.5-aikido.2"},{"fixed":"2.2.1-aikido.2"}]}]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.0-1"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.0-2","2.2.1-1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.1-1","2.2.1-2","3.0.1+~3.0.0-2"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.1+~3.0.0-3"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.1+~3.0.0-3"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.1+~3.0.0-3","3.0.7+~3.0.6-2","3.0.8+~3.0.6-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"node-js-cookie","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.1+~3.0.0-3"]}],"products":[{"vendor":"js-cookie","product":"javascript_cookie"},{"vendor":"js-cookie","product":"js-cookie"},{"vendor":"red hat","product":"cryostat 4 on rhel 9"},{"vendor":"red hat","product":"openshift lightspeed"},{"vendor":"red hat","product":"red hat 3scale api management platform 2"},{"vendor":"red hat","product":"red hat advanced cluster security for kubernetes 4.10"},{"vendor":"red hat","product":"red hat ansible automation platform 2"},{"vendor":"red hat","product":"red hat ansible automation platform 2.1"},{"vendor":"red hat","product":"red hat ansible automation platform 2.2"},{"vendor":"red hat","product":"red hat ansible automation platform 2.7"},{"vendor":"red hat","product":"red hat developer hub 1.10"},{"vendor":"red hat","product":"red hat developer hub 1.9"},{"vendor":"red hat","product":"red hat discovery 2"},{"vendor":"red hat","product":"red hat enterprise linux 10"},{"vendor":"red hat","product":"red hat enterprise linux 8"},{"vendor":"red hat","product":"red hat enterprise linux 9"},{"vendor":"red hat","product":"red hat jboss enterprise application platform 7"},{"vendor":"red hat","product":"red hat jboss enterprise application platform 8"},{"vendor":"red hat","product":"red hat jboss enterprise application platform expansion pack"},{"vendor":"red hat","product":"red hat openshift ai (rhoai)"},{"vendor":"red hat","product":"red hat openshift ai 3.4"},{"vendor":"red hat","product":"red hat openshift container platform 4"},{"vendor":"red hat","product":"red hat openshift service mesh 3.3"},{"vendor":"redhat","product":"3scale_api_management"},{"vendor":"redhat","product":"ansible_automation_platform"},{"vendor":"redhat","product":"enterprise_linux"},{"vendor":"redhat","product":"openshift_ai"},{"vendor":"redhat","product":"openshift_lightspeed"}],"references":[{"url":"https://github.com/js-cookie/js-cookie/security/advisories/GHSA-qjx8-664m-686j","tags":["x_refsource_CONFIRM","exploit","Exploit","Vendor Advisory","advisory","web","report"]},{"url":"https://github.com/js-cookie/js-cookie/commit/eb3c40e89731e99b8970faaf35ddad249c6c0020","tags":["x_refsource_MISC","Patch","fix","web","report"]},{"url":"https://github.com/js-cookie/js-cookie/releases/tag/v3.0.7","tags":["x_refsource_MISC","Release Notes","web","report"]},{"url":"https://access.redhat.com/security/cve/CVE-2026-46625","tags":["vdb-entry","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2487740","tags":["issue-tracking","x_refsource_REDHAT","Issue Tracking","Third Party Advisory","report"]},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-46625.json","tags":["x_sadp-csaf-vex","Third Party Advisory","web"]},{"url":"https://access.redhat.com/errata/RHSA-2026:48151","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:36625","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:56338","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:56357","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:59153","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:48126","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:49642","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:52768","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:60520","tags":["vendor-advisory","x_refsource_REDHAT","advisory"]},{"url":"https://access.redhat.com/errata/RHSA-2026:33183","tags":["vendor-advisory","x_refsource_REDHAT","Third Party Advisory","advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46625","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-qjx8-664m-686j"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46625.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-46625","tags":["advisory"]},{"url":"https://github.com/js-cookie/js-cookie","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2026-46625","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-46625","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-46625","title":"JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","status":"published","published":"2026-06-10T21:18:05.372Z","modified":"2026-09-09T12:05:08.819Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high","assessor":"cna"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high","assessor":"adp"}],"cwes":["CWE-1321","CWE-915"],"updated_at":"2026-11-02T13:46:55.086623Z"}],"euvd":[{"id":"EUVD-2026-36154","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","status":"published","published":"2026-06-10T21:18:05Z","modified":"2026-09-09T12:05:08Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"updated_at":"2026-11-02T17:28:27.763941Z"}],"ghsa":[{"id":"GHSA-qjx8-664m-686j","title":"JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection","description":"## 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 =\u003e 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 \u003c 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 \u0026\u0026 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\u003cimg width=\"2614\" height=\"1174\" alt=\"cls-2026-05-14-01 44 39\" src=\"https://github.com/user-attachments/assets/120df1fe-7e97-4ca3-904e-ab80d71ecf62\" /\u003e\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 \u003c 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```","status":"published","published":"2026-05-21T21:20:31Z","modified":"2026-06-11T14:05:07Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T14:40:26.12116Z"}],"nvd":[{"id":"CVE-2026-46625","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","status":"published","published":"2026-06-10T22:16:59.613Z","modified":"2026-09-09T13:20:18.357Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high","assessor":"secondary"}],"cwes":["CWE-1321","CWE-915"],"updated_at":"2026-11-02T14:12:23.485267Z"}],"osv":[{"id":"CVE-2026-46625","title":"JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","status":"published","published":"2026-06-10T21:18:05.372Z","modified":"2026-10-28T02:30:44.410401804Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T15:45:06.231145Z"},{"id":"DEBIAN-CVE-2026-46625","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","status":"published","published":"2026-06-10T22:16:59.613Z","modified":"2026-10-01T03:02:33.890801993Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"updated_at":"2026-11-02T15:45:56.444225Z"},{"id":"GHSA-qjx8-664m-686j","title":"JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection","description":"## 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 =\u003e 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 \u003c 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 \u0026\u0026 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\u003cimg width=\"2614\" height=\"1174\" alt=\"cls-2026-05-14-01 44 39\" src=\"https://github.com/user-attachments/assets/120df1fe-7e97-4ca3-904e-ab80d71ecf62\" /\u003e\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 \u003c 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```","status":"published","published":"2026-05-21T21:20:31Z","modified":"2026-09-10T03:50:47.374021767Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"cwes":["CWE-1321"],"updated_at":"2026-11-02T15:46:54.760124Z"},{"id":"ROOT-APP-NPM-CVE-2026-46625","title":"CVE-2026-46625 in @rootio/js-cookie - Patched by Root","description":"Root has patched CVE-2026-46625 in the @rootio/js-cookie package for Root:npm. Multiple fixed versions available.","status":"published","published":"2026-06-04T19:48:41Z","modified":"2026-06-05T01:30:48.173863184Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"updated_at":"2026-11-02T15:53:27.649662Z"},{"id":"UBUNTU-CVE-2026-46625","description":"JavaScript Cookie is a JavaScript API for handling cookies, client-side. Prior to version 3.0.7, 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. Because 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. This issue has been patched in version 3.0.7.","status":"published","published":"2026-06-10T22:16:00Z","modified":"2026-10-17T12:58:24.946496902Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"high"}],"updated_at":"2026-11-02T16:56:30.797112Z"},{"id":"CLSA-2026-1782089812","title":"TuxCare security update for js-cookie (1 CVE)","description":"TuxCare rebuilt js-cookie to address 1 CVE. Fixed in 2.2.1-tuxcare.1.","status":"published","published":"2026-08-04T14:52:38Z","modified":"2026-10-15T09:47:09.337032496Z","updated_at":"2026-11-02T15:43:45.794021Z"}]}}