Valibot: record() issue paths can make flatten() throw for inherited Object property names

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-59952: 0.38% estimated exploitation activity in the next 30 days; percentile 32.40 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary valibot 1.4.1 can throw a TypeError inside its flatten() helper when validation issues contain attacker-controlled object keys such as toString, valueOf, or hasOwnProperty. The issue is reachable through normal record() validation. record() intentionally filters proto, prototype, and constructor, but it still accepts other own keys that collide with inherited Object.prototype properties. If the record key schema or value schema rejects such an entry, Valibot creates an issue path containing that key. Passing the resulting issues to Valibot's documented flatten() helper causes flatErrors.nested[dotPath] to resolve to the inherited method instead of an own error array, and the helper calls .push(...) on that function. This is not a global prototype pollution issue. The impact is availability/error handling: applications that validate user-controlled objects with record() and flatten validation errors for API responses can crash the request path with a TypeError instead of…

Published by the source

24 Jul 2026, 16:14 UTC

Last modified by the source

24 Jul 2026, 16:33 UTC

Source last checked

26 Oct 2026, 12:58 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-5qjj-4xww-7phc

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-5qjj-4xww-7phc

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# Patch Next advisory brief: CVE-2026-59952

Advisory: Valibot: record() issue paths can make flatten() throw for inherited Object property names
IDs: CVE-2026-59952, GHSA-5qjj-4xww-7phc
Record: https://patchnext.com/advisories/cve-2026-59952 (revision 3, source checked 26 Oct 2026, 12:58 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: valibot 1.4.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm valibot: affected <= 1.4.1; fixed in 1.4.2

## Suggested inspection (read-only)
- `npm ls valibot --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on valibot.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-5qjj-4xww-7phc (OSV record GHSA-5qjj-4xww-7phc lists affected ranges: npm valibot >=0 <1.4.2 (fixed))
- Verified: https://github.com/advisories/GHSA-5qjj-4xww-7phc (GitHub-reviewed advisory GHSA-5qjj-4xww-7phc lists affected ranges: npm valibot >=0 <=1.4.1)

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