Secuno
ENNL
Book demo

CVE-2025-66456

Elysiajs Elysia vulnerability

9.8 CRITICALPublic exploitEPSS 0.56%
  1. Published9 Dec 2025

Description

Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation and client-server communication. Versions 1.4.0 through 1.4.16 contain a prototype pollution vulnerability in `mergeDeep` after merging results of two standard schema validations with the same key. Due to the ordering of merging, there must be an any type that is set as a standalone guard, to allow for the `__proto__ prop` to be merged. When combined with GHSA-8vch-m3f4-q8jf this allows for a full RCE by an attacker. This issue is fixed in version 1.4.17. To workaround, remove the `__proto__ key` from body.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Elysiajs Elysia≥ 1.4.0 < 1.4.17

Remediation

Fixed in
Elysiajs Elysia≥ 1.4.17

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

CVE-2021-480128.2
fast-toml through 0.5.4 contains a prototype pollution vulnerability that allows…
CVE-2026-1077018.2
dot-access through 1.0.0 contains a prototype pollution vulnerability that allows…
CVE-2026-1058588.1
Payload is a free and open source headless content management system. In versions…
CVE-2026-10585710.0
Payload is a free and open source headless content management system. In…
CVE-2026-615349.1
Yayson is a library for serializing and reading JSON API data in JavaScript. Prior to…
CVE-2026-819948.2
Acrobat Reader is affected by an Improperly Controlled Modification of Object Prototype…

Frequently asked

Is CVE-2025-66456 being actively exploited?

CVE-2025-66456 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.56%.

How severe is CVE-2025-66456?

CVE-2025-66456 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.56% probability of exploitation.

Which products are affected by CVE-2025-66456?

Affected products include Elysiajs Elysia.

How do I fix CVE-2025-66456?

Upgrade affected software to a fixed version, for example Elysiajs Elysia 1.4.17 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-66456 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

Get Patch this first every Monday

Five vulnerabilities that matter this week, ranked on real exploitation. Plain language, one email, no spam.

You can unsubscribe with one click from every issue. We handle your details as described in our privacy policy.

Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.