Apostrophe has Server-Side Prototype Pollution in apos.util.set via patch operators that leads to process-wide authorization bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-53609: 0.35% estimated exploitation activity in the next 30 days; percentile 28.18 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

<img width="1919" height="1046" alt="proto" src="https://github.com/user-attachments/assets/c5c69718-6448-448d-b64b-e3db41ab6ff6" / Summary apos.util.set() traverses dot-notation paths without sanitizing proto, allowing an authenticated editor to write arbitrary values to Object.prototype via the $pullAll patch operator. A confirmed gadget in publicApiCheck() causes this to bypass authorization on all piece-type REST API endpoints for every subsequent unauthenticated request, for the lifetime of the Node.js process. --- Details Root Cause — apos.util.set() (modules/@apostrophecms/util/index.js ~line 800) The function splits a dot-notation path and traverses properties without rejecting proto, constructor, or prototype: Source — implementPatchOperators() (modules/@apostrophecms/schema/index.js ~line 1737) User-controlled keys from the $pullAll operator are passed directly to apos.util.set(): cloneOriginalBase() does not sanitize proto because .has() performs an own-property check.…

Published by the source

31 Jul 2026, 21:49 UTC

Last modified by the source

31 Jul 2026, 22:00 UTC

Source last checked

26 Oct 2026, 13:00 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-6h5j-32cf-4253

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-6h5j-32cf-4253

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-6h5j-32cf-4253

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# Patch Next advisory brief: CVE-2026-53609

Advisory: Apostrophe has Server-Side Prototype Pollution in apos.util.set via patch operators that leads to process-wide authorization bypass
IDs: CVE-2026-53609, GHSA-6h5j-32cf-4253
Record: https://patchnext.com/advisories/cve-2026-53609 (revision 3, source checked 26 Oct 2026, 13:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: apostrophe 4.31.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm apostrophe: affected <= 4.30.0; fixed in 4.31.0

## Suggested inspection (read-only)
- `npm ls apostrophe --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 apostrophe.
- 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://github.com/advisories/GHSA-6h5j-32cf-4253 (GitHub-reviewed advisory GHSA-6h5j-32cf-4253 lists affected ranges: npm apostrophe >=0 <=4.30.0)
- Verified: https://osv.dev/vulnerability/GHSA-6h5j-32cf-4253 (OSV record GHSA-6h5j-32cf-4253 lists affected ranges: npm apostrophe >=0 <4.31.0 (fixed))

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