CVE-2025-66456

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 61% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this weekElevated
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.8Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
9.8
EG Score
9.8(medium)
EG Risk
60(Track*)
EG Risk 60/100SSVC: Track*

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS
38.6%
KEV
Not listed

Published

December 9, 2025

Last Modified

June 17, 2026

Advisory Details (5)

Auto-updated Jun 21, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github_pr, github.
github Patch Available🟡 PoC Available

Prototype pollution with multiple standalone validation schemas · Advisory · elysiajs/elysia · GitHub

https://github.com/elysiajs/elysia/security/advisories/GHSA-hxj9-33pp-j2cc
github Patch Available🟡 PoC Available

Arbitrary code injection through cookie config · Advisory · elysiajs/elysia · GitHub

https://github.com/elysiajs/elysia/security/advisories/GHSA-8vch-m3f4-q8jf
github_pr Patch Available

patch 1.4.17

Patch available: elysiajs/elysia 1.4.17 (PR #1564 merged 2025-12-02)

https://github.com/elysiajs/elysia/pull/1564
github_commit Patch Available

commit 3af978663e43 (elysiajs/elysia)

Patch available: elysiajs/elysia 1.4.17 (contains commit 3af978663e43)

https://github.com/elysiajs/elysia/commit/3af978663e437dccc6c1a2a3aff4b74e1574849e
github_commit Patch Available

commit 26935bf76ebc (elysiajs/elysia)

Patch available: elysiajs/elysia 1.4.17 (contains commit 26935bf76ebc)

https://github.com/elysiajs/elysia/commit/26935bf76ebc43b4a43d48b173fc853de43bb51e

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFixed inDependents
elysia—1.4.17—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 13× in last 7d / 48× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-23 14:18 UTCEPSS rescore
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  3. 2026-07-23 13:19 UTCOSV refresh
  4. 2026-07-23 03:01 UTCEG score recompute
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  1. 2026-07-06 16:27 UTCEPSS rescore
  2. 2026-07-06 08:11 UTCOSV refresh
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  66. 2026-05-29 18:02 UTCEG score recompute
  67. 2026-05-29 13:44 UTCEPSS rescore

Frequently asked(5)

What is CVE-2025-66456?
CVE-2025-66456 is a critical vulnerability published on December 9, 2025. 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…
When was CVE-2025-66456 disclosed?
CVE-2025-66456 was first published in the National Vulnerability Database on December 9, 2025, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2025-66456 actively exploited?
CVE-2025-66456 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 38.6% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2025-66456?
CVE-2025-66456 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2025-66456?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2025-66456, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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