What is the CVSS score of CVE-2026-53609?

CVE-2026-53609 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:L. EPSS exploitation probability: 0.1%.

Which versions of ApostropheCMS are affected by CVE-2026-53609?

ApostropheCMS versions 4.30.0 and earlier contain a critical prototype pollution vulnerability that allows authenticated editors to permanently poison Object.prototype, enabling complete…. A patch is available.

How to fix or mitigate CVE-2026-53609?

Within 24 hours: Audit all ApostropheCMS instances; identify which are internet-facing and restrict editor account access to internal networks only. Within 7 days: Implement network segmentation to isolate editor interfaces; enable API access logging and establish monitoring for unauthorized requests; contact Apostrophe development team to confirm patch timeline. Within 30 days: Evaluate whether any patched version (>4.30.0) is available for upgrade; if not, prepare contingency plan for disabling REST API or full application redesign.

ApostropheCMS CVE-2026-53609

EUVD-2026-36590 CRITICAL

Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution) (CWE-1321)

2026-06-12 GitHub_M

GHSA-6h5j-32cf-4253

Prototype Pollution Authentication Bypass Node.js Apostrophe

9.1

CVSS 3.1 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:L

vuln.today AI

9.1 CRITICAL

Network-reachable editor endpoint (AV:N, PR:L, UI:N); pollution subverts a separate auth component (S:C); resulting anonymous API access yields high confidentiality but only low integrity/availability impact.

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

4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:H/SI:L/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

Low

Availability

Low

Lifecycle Timeline

Analysis Generated

Jun 12, 2026 - 22:15 vuln.today

DescriptionCVE.org

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.

Articles & Coverage 1

News Critical Prototype Pollution in ApostropheCMS 4.30.0 - CVE-2026-53609 Jun 12, 2026

AnalysisAI

Prototype pollution in ApostropheCMS versions up to and including 4.30.0 allows an authenticated editor to poison Object.prototype via the $pullAll patch operator, ultimately bypassing authorization on all piece-type REST API endpoints for unauthenticated requests until the Node.js process restarts. The flaw stems from apos.util.set() failing to sanitize __proto__ in dot-notation paths, and no public exploit identified at time of analysis but the advisory describes a confirmed exploitation gadget in publicApiCheck(). No vendor-released patch identified at time of analysis, making this an open-window risk for any internet-exposed editor account.

Technical ContextAI

ApostropheCMS is a Node.js-based open-source content management system whose editing API exposes a generic patch mechanism for piece-type documents. The vulnerable apos.util.set() helper walks user-supplied dot-notation property paths to assign values without filtering reserved JavaScript property names such as __proto__, constructor, or prototype - the canonical CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes / 'Prototype Pollution') pattern. When the $pullAll patch operator is used against an editor-accessible endpoint, the attacker-controlled keys reach this sink and mutate Object.prototype itself. The advisory identifies a specific gadget in publicApiCheck() - the function that decides whether a REST request requires authentication - meaning a polluted property on Object.prototype is read as if it were a configured value on the check object, flipping the authorization decision for the lifetime of the process (cpe:2.3:a:apostrophecms:apostrophe:*).

RemediationAI

No vendor-released patch identified at time of analysis - the advisory explicitly states no patched versions are available, so monitor https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-6h5j-32cf-4253 and apply the fix immediately once published. Compensating controls until then: tightly restrict who holds the editor role and disable open registration for editor-level accounts (trade-off: blocks legitimate contributor onboarding); place the admin and piece-type REST API endpoints behind an authenticated reverse proxy or IP allowlist so that even a polluted publicApiCheck() cannot serve anonymous traffic (trade-off: breaks intentionally public APIs); filter $pullAll patch bodies at a WAF or middleware to drop any path token containing __proto__, constructor, or prototype (trade-off: bypassable via unicode or unusual encodings and may break legitimate keys); and schedule frequent Node.js process restarts so any successful pollution is short-lived (trade-off: brief downtime and does not prevent re-exploitation).