CVE-2025-66456
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedElysia 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceElysia framework versions 1.4.0-1.4.16 contain a prototype pollution vulnerability in the `mergeDeep` function. When merging schema validation results with the same key containing an 'any' type guard, attackers can inject `__proto__` properties. This can be chained with GHSA-8vch-m3f4-q8jf to achieve full RCE.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 1.4.0, < 1.4.17CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Elysia versionRun `npm list elysia` or check your package.json for the @elysiajs/elysia dependency versionAffected if Version is >= 1.4.0 and < 1.4.17
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Identify use of mergeDeep with schema validationSearch codebase for imports or usage of `mergeDeep` function from Elysia, and examine schema validation definitions using the `any` typeAffected if Code uses standard schema validation with `any` type as a standalone guard in the same key across multiple merge operations
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Inspect request handling for proto keysReview request body parsing logic to see if incoming JSON payloads could contain `__proto__` or `constructor.prototype` keys before validation occursAffected if Application accepts arbitrary JSON bodies without stripping prototype properties before schema validation
You are affected if your Elysia version is between 1.4.0 and 1.4.16 inclusive and your application uses standard schema validation with `any` type guards while accepting user-controlled request bodies.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped1.4.17
Upgrade to Elysia version 1.4.17 or later. Alternatively, implement input validation to strip `__proto__` keys from request bodies before processing.
1.4.17
- Update the Elysia package to version 1.4.17 or later by running `npm install elysia@^1.4.17` or `yarn add elysia@^1.4.17`
- After upgrading, verify that the application functions correctly with the new version
- Test that the prototype pollution vulnerability is mitigated by ensuring `__proto__` properties in request bodies are handled safely
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2025-66456 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-66456 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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