CVE-2025-66456: Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation and client-serv

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CRITICAL 9.8REMOTEUPGRADE

CVE-2025-66456 is a critical-severity flaw (CVSS 9.8) affecting elysia. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 wi

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 53%)
CISA exploited list	No
Weakness	CWE-1321
Published	2025-12-09
Last modified	2026-10-14

Publisher (CNA): GitHub, Inc. · Vendor: elysiajs

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-09 20:15 UTCPublished CVE record published
2026-10-14 21:10 UTCUpdated Record last modified

elysiajs elysia UPGRADE

Affected: >= 1.4.0 and < 1.4.17

Fixed in: 1.4.17

Safe to downgrade to: a release before 1.4.0

1. Check installed version

npm ls elysia

2. UPGRADE to 1.4.17

npm install elysia@">=1.4.17"

3. If no update is available yet, DOWNGRADE to a release before 1.4.0

npm view elysia versions npm install elysia@"<1.4.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

npm · elysia · FIXED · 1.4.17 · vulnerable: >= 1.4.0, < 1.4.17 · source

npm install elysia@">=1.4.17" npm ls elysia

Fedora ELN · openjpeg · FIXED · 2.5.4-5.eln159 · FEDORA-2026-1a5f60f401 · source

sudo dnf upgrade --advisory=FEDORA-2026-1a5f60f401

Fedora 46 · trustedqsl · FIXED · 2.8.7-1.fc46 · FEDORA-2026-6b1bc90ebc · source

sudo dnf upgrade --advisory=FEDORA-2026-6b1bc90ebc

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/elysiajs/elysia/pull/1564
Write-up: github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf
Write-up: github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-66456?

elysia: upgrade to 1.4.17. Exact commands for each OS are on this page.

Is CVE-2025-66456 being exploited?

CVE-2025-66456 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-66456 affect?

CVE-2025-66456 affects elysia. Severity is critical (CVSS 9.8). 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 o

How urgent is CVE-2025-66456?

Priority 56/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2025-66457 HIGH 8.8 UPGRADE Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation and client-serv
CVE-2026-31865 MEDIUM 6.5 UPGRADE Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-ser
CVE-2026-30837 HIGH 7.5 UPGRADE Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation and client-serv

References

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