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High, CVSS 7.5amended

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

CVE-2026-46625GHSA-qjx8-664m-686j

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (js-cookie 3.0.7), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS
  • CVE-2026-46625: 0.92% estimated exploitation activity in the next 30 days; percentile 60.31 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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,…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-qjx8-664m-686j

  2. Revision 1 · created ·

    Published from osv record GHSA-qjx8-664m-686j

Agent brief

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# Patch Next advisory brief: CVE-2026-46625

Advisory: JavaScript Cookie: Per-instance prototype hijack in assign() enables cookie-attribute injection
IDs: CVE-2026-46625, GHSA-qjx8-664m-686j
Record: https://patchnext.com/advisories/cve-2026-46625 (revision 2, source checked 26 Oct 2026, 12:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: js-cookie 3.0.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm js-cookie: affected <= 3.0.5; fixed in 3.0.7

## Suggested inspection (read-only)
- `npm ls js-cookie --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on js-cookie.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-qjx8-664m-686j (OSV record GHSA-qjx8-664m-686j lists affected ranges: npm js-cookie >=0 <3.0.7 (fixed))
- Verified: https://github.com/advisories/GHSA-qjx8-664m-686j (GitHub-reviewed advisory GHSA-qjx8-664m-686j lists affected ranges: npm js-cookie >=0 <=3.0.5)

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