CVE-2026-53609
CVE-2026-53609 is a critical-severity vulnerability with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1321.
Key facts
- Severity: Critical (CVSS 3.x base score 9.1)
- EPSS exploit prediction: 0% (15th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-36590
- Weakness: CWE-1321
- Published:
- Last modified:
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 `$pullAll` patch operator. A confirmed gadget in `publicApiCheck()` causes this to bypass authorization on all piece-type REST API endpoints for every subsequent unauthenticated request, for the lifetime of the Node.js process. As of time of publication, no known patched versions are available.
Frequently asked questions
- What is CVE-2026-53609?
- ApostropheCMS is an open-source Node.js content management system. In versions up to and including 4.30.0, `apos.util.set()` traverses dot-notation paths without sanitizing `__proto__`, allowing an authenticated editor to write arbitrary values to `Object.prototype` via the `$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.
- How severe is CVE-2026-53609?
- CVE-2026-53609 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity low, and availability low.
- Is CVE-2026-53609 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-53609?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
- Does CVE-2026-53609 have an EU (EUVD) identifier?
- Yes. CVE-2026-53609 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-36590.
- When was CVE-2026-53609 published?
- CVE-2026-53609 was published on 2026-06-12 and last updated on 2026-06-17.
References
Other CWE-1321 (Prototype Pollution) vulnerabilities
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