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

Vulnerability summary

CVE-2026-53609 is a critical (CVSS 9.1) Prototype Pollution vulnerability in apostrophecms apostrophe. EPSS estimates a 0.38% chance of exploitation in the next 30 days, higher than 30.7% of scored vulnerabilities.

Timeline

1. 12-06-2026
   PublishedVulnerability first disclosed.
2. 15-06-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-1321Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.