---
title: "CVE-2026-53609: Apostrophe has Server-Side Prototype Pollution in apos.util.set via patch operators that leads to process-wide authorization bypass"
url: https://erroneo.us/security/cve/CVE-2026-53609/
description: "CVE-2026-53609 (apostrophe (npm)): ApostropheCMS is an open-source Node.js content management system. In versions up to and including 4.30.0…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-06-12
date_modified: 2026-07-31
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-53609"
kev: false
cvss: 9.1
epss: 0.0038
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-53609: Apostrophe has Server-Side Prototype Pollution in apos.util.set via patch operators that leads to process-wide authorization bypass

**Signal:** Critical, preconditions apply. Severe if exploited, but exploitation needs conditions that may not apply to you. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.4% , percentile 31: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 31% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.
- Only applies if your dependency tree includes apostrophe (npm) <= 4.30.0, fixed in 4.31.0 . Check your lockfile, including transitive dependencies.

## What it is

ApostropheCMS is an open-source Node.js content management system. In versions up to and including 4.30.0, 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. As of time of publication, no known patched versions are available.

## Affected packages

- npm `apostrophe` <= 4.30.0 → fixed: 4.31.0

## Affected products (CVE record)

- apostrophecms apostrophe: <= 4.30.0

## Severity

- GitHub_M CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:L`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:L`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 0.38% probability of exploitation activity in the next 30 days; percentile 31.

## Sources

- [GitHub Advisory GHSA-6h5j-32cf-4253](https://github.com/advisories/GHSA-6h5j-32cf-4253)
- [CVE.org record CVE-2026-53609](https://www.cve.org/CVERecord?id=CVE-2026-53609)
- [NVD entry CVE-2026-53609](https://nvd.nist.gov/vuln/detail/CVE-2026-53609)
- [github.com](https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-6h5j-32cf-4253)
- [github.com](https://github.com/apostrophecms/apostrophe/pull/5464)
- [github.com](https://github.com/apostrophecms/apostrophe/commit/5a88e9630cbbdde33154ef8abe7557ddf7be418b)

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Source page: https://erroneo.us/security/cve/CVE-2026-53609/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt