Vulnerability-Lookup

GHSA-5QJJ-4XWW-7PHC

Vulnerability from github – Published: 2026-07-24 16:14 – Updated: 2026-07-24 16:14

Summary

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

Details

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 returning structured validation errors.

Affected package

Ecosystem: npm
Package: valibot
Affected version verified: 1.4.1
Fixed version: none known
Repository: open-circle/valibot
Current main ref tested by source review: 9bb6617

Root cause

record() uses _isValidObjectKey() before validating record entries. The helper blocks the three classic prototype pollution keys:

key !== '__proto__' &&
key !== 'prototype' &&
key !== 'constructor'

It does not block other inherited Object.prototype names such as toString, valueOf, and hasOwnProperty. These remain valid own JSON object keys and can appear in issue paths when either the record key schema or value schema rejects the entry.

flatten() then creates nested error storage with an ordinary object:

flatErrors.nested = {};

For a dot path such as toString, this check reads the inherited Object.prototype.toString function:

if (flatErrors.nested![dotPath]) {
  flatErrors.nested![dotPath]!.push(issue.message);
}

Because the inherited function is truthy, flatten() calls .push(...) on a function and throws TypeError: flatErrors.nested[dotPath].push is not a function.

Impact

A remote attacker can trigger this if an application:

validates attacker-controlled JSON objects with v.record(...);
receives an invalid key or invalid value under a key such as toString;
uses Valibot's flatten(result.issues) helper to prepare validation errors.

This is a common pattern in API/form validation: safeParse() collects issues and flatten() converts them into response-friendly error objects. Instead of a validation response, the request can hit an unexpected exception path.

The same root cause can also affect manually constructed issues or other schemas that place inherited Object property names into dot paths. I am reporting the record() path because it uses only public Valibot APIs and attacker-controlled JSON keys.

Local reproduction

Run in a disposable directory:

npm install valibot@1.4.1
node poc_record_flatten_inherited_key_dos.mjs

Minimal example:

import * as v from 'valibot';

const schema = v.record(v.string(), v.number());
const input = JSON.parse('{"toString":"not-a-number"}');

const result = v.safeParse(schema, input);
console.log(result.success); // false
console.log(result.issues[0].path.map((item) => item.key)); // ["toString"]

v.flatten(result.issues); // TypeError

Observed output from valibot@1.4.1:

{
  "name": "record value schema rejects attacker-controlled value",
  "key": "toString",
  "success": false,
  "issueCount": 1,
  "firstPath": ["toString"],
  "firstMessage": "Invalid type: Expected number but received \"not-a-number\"",
  "flattened": {
    "ok": false,
    "exception": "TypeError",
    "message": "flatErrors.nested[dotPath].push is not a function"
  }
}

The local PoC also reproduces the same exception for valueOf, hasOwnProperty, isPrototypeOf, propertyIsEnumerable, and toLocaleString. A control case with an ordinary key produces normal flattened errors.

Duplicate checks performed before submission

npm metadata confirmed current valibot release is 1.4.1 and maps to open-circle/valibot.
gh api repos/open-circle/valibot/private-vulnerability-reporting returned {"enabled":true}.
npm audit for a clean project containing only valibot@1.4.1 returned no vulnerabilities.
Repository advisories and the GitHub Advisory Database only returned the historical emoji ReDoS advisory fixed in 1.2.0.
OSV exact-version query for npm valibot 1.4.1 returned no vulnerabilities.
Public issue/PR searches for flatten toString, flatten hasOwnProperty, record toString, __proto__, constructor, and prototype pollution did not find a matching disclosure of this record() issue-path / flatten() exception.
Reviewed related public PRs: open-circle/valibot#67 added prototype pollution mitigation for record() by blacklisting __proto__, prototype, and constructor; it does not cover flatten() collisions with other inherited property names. open-circle/valibot#1429 is an open plain-object / record() type semantics PR and does not disclose this flatten() exception behavior.

Suggested remediation

Use null-prototype containers for flat error maps and/or perform own-property checks before appending:

Initialize flatErrors.nested as Object.create(null).
Check nested entries with Object.prototype.hasOwnProperty.call(flatErrors.nested, dotPath) rather than truthiness.
Consider filtering or escaping unsafe dot path segments in getDotPath() / flatten(), including inherited Object property names.
Add regression tests for flatten() with paths toString, valueOf, hasOwnProperty, __proto__, prototype, and constructor.
Consider using the same hardening for other accumulator objects that store attacker-controlled keys.

Severity

6.9 (Medium)


                  
                    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

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.4.1"
      },
      "package": {
        "ecosystem": "npm",
        "name": "valibot"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.4.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-59952"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-755"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-24T16:14:31Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "## Summary\n\n`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`.\n\nThe 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\u0027s 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.\n\nThis 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 returning structured validation errors.\n\n## Affected package\n\n- Ecosystem: npm\n- Package: `valibot`\n- Affected version verified: `1.4.1`\n- Fixed version: none known\n- Repository: `open-circle/valibot`\n- Current main ref tested by source review: `9bb6617`\n\n## Root cause\n\n`record()` uses `_isValidObjectKey()` before validating record entries. The helper blocks the three classic prototype pollution keys:\n\n```ts\nkey !== \u0027__proto__\u0027 \u0026\u0026\nkey !== \u0027prototype\u0027 \u0026\u0026\nkey !== \u0027constructor\u0027\n```\n\nIt does not block other inherited `Object.prototype` names such as `toString`, `valueOf`, and `hasOwnProperty`. These remain valid own JSON object keys and can appear in issue paths when either the record key schema or value schema rejects the entry.\n\n`flatten()` then creates nested error storage with an ordinary object:\n\n```ts\nflatErrors.nested = {};\n```\n\nFor a dot path such as `toString`, this check reads the inherited `Object.prototype.toString` function:\n\n```ts\nif (flatErrors.nested![dotPath]) {\n  flatErrors.nested![dotPath]!.push(issue.message);\n}\n```\n\nBecause the inherited function is truthy, `flatten()` calls `.push(...)` on a function and throws `TypeError: flatErrors.nested[dotPath].push is not a function`.\n\n## Impact\n\nA remote attacker can trigger this if an application:\n\n1. validates attacker-controlled JSON objects with `v.record(...)`;\n2. receives an invalid key or invalid value under a key such as `toString`;\n3. uses Valibot\u0027s `flatten(result.issues)` helper to prepare validation errors.\n\nThis is a common pattern in API/form validation: `safeParse()` collects issues and `flatten()` converts them into response-friendly error objects. Instead of a validation response, the request can hit an unexpected exception path.\n\nThe same root cause can also affect manually constructed issues or other schemas that place inherited Object property names into dot paths. I am reporting the `record()` path because it uses only public Valibot APIs and attacker-controlled JSON keys.\n\n## Local reproduction\n\nRun in a disposable directory:\n\n```bash\nnpm install valibot@1.4.1\nnode poc_record_flatten_inherited_key_dos.mjs\n```\n\nMinimal example:\n\n```js\nimport * as v from \u0027valibot\u0027;\n\nconst schema = v.record(v.string(), v.number());\nconst input = JSON.parse(\u0027{\"toString\":\"not-a-number\"}\u0027);\n\nconst result = v.safeParse(schema, input);\nconsole.log(result.success); // false\nconsole.log(result.issues[0].path.map((item) =\u003e item.key)); // [\"toString\"]\n\nv.flatten(result.issues); // TypeError\n```\n\nObserved output from `valibot@1.4.1`:\n\n```json\n{\n  \"name\": \"record value schema rejects attacker-controlled value\",\n  \"key\": \"toString\",\n  \"success\": false,\n  \"issueCount\": 1,\n  \"firstPath\": [\"toString\"],\n  \"firstMessage\": \"Invalid type: Expected number but received \\\"not-a-number\\\"\",\n  \"flattened\": {\n    \"ok\": false,\n    \"exception\": \"TypeError\",\n    \"message\": \"flatErrors.nested[dotPath].push is not a function\"\n  }\n}\n```\n\nThe local PoC also reproduces the same exception for `valueOf`, `hasOwnProperty`, `isPrototypeOf`, `propertyIsEnumerable`, and `toLocaleString`. A control case with an ordinary key produces normal flattened errors.\n\n## Duplicate checks performed before submission\n\n- npm metadata confirmed current `valibot` release is `1.4.1` and maps to `open-circle/valibot`.\n- `gh api repos/open-circle/valibot/private-vulnerability-reporting` returned `{\"enabled\":true}`.\n- `npm audit` for a clean project containing only `valibot@1.4.1` returned no vulnerabilities.\n- Repository advisories and the GitHub Advisory Database only returned the historical emoji ReDoS advisory fixed in `1.2.0`.\n- OSV exact-version query for npm `valibot` `1.4.1` returned no vulnerabilities.\n- Public issue/PR searches for `flatten toString`, `flatten hasOwnProperty`, `record toString`, `__proto__`, `constructor`, and `prototype pollution` did not find a matching disclosure of this `record()` issue-path / `flatten()` exception.\n- Reviewed related public PRs: `open-circle/valibot#67` added prototype pollution mitigation for `record()` by blacklisting `__proto__`, `prototype`, and `constructor`; it does not cover `flatten()` collisions with other inherited property names. `open-circle/valibot#1429` is an open plain-object / `record()` type semantics PR and does not disclose this `flatten()` exception behavior.\n\n## Suggested remediation\n\nUse null-prototype containers for flat error maps and/or perform own-property checks before appending:\n\n- Initialize `flatErrors.nested` as `Object.create(null)`.\n- Check nested entries with `Object.prototype.hasOwnProperty.call(flatErrors.nested, dotPath)` rather than truthiness.\n- Consider filtering or escaping unsafe dot path segments in `getDotPath()` / `flatten()`, including inherited Object property names.\n- Add regression tests for `flatten()` with paths `toString`, `valueOf`, `hasOwnProperty`, `__proto__`, `prototype`, and `constructor`.\n- Consider using the same hardening for other accumulator objects that store attacker-controlled keys.",
  "id": "GHSA-5qjj-4xww-7phc",
  "modified": "2026-07-24T16:14:31Z",
  "published": "2026-07-24T16:14:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/open-circle/valibot/security/advisories/GHSA-5qjj-4xww-7phc"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-circle/valibot/pull/1522"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-circle/valibot/commit/1bd01c304657cd0809cc92694360b6cc60f700bf"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/open-circle/valibot"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-circle/valibot/releases/tag/v1.4.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Valibot: record() issue paths can make flatten() throw for inherited Object property names"
}

CVE-2026-59952 (GCVE-0-2026-59952)

Vulnerability from cvelistv5 – Published: 2026-07-30 00:10 – Updated: 2026-07-30 00:10

Title

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

Summary

Valibot helps validate data using a schema. Versions prior to 1.4.2 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 returning structured validation errors. This issue has been fixed in version 1.4.2.

Severity

6.9 (Medium)


                        
                          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

CWE

CWE-755 - Improper Handling of Exceptional Conditions

Assigner

GitHub_M

References

4 references

URL	Tags
https://github.com/open-circle/valibot/security/a…	x_refsource_CONFIRM
https://github.com/open-circle/valibot/pull/1522	x_refsource_MISC
https://github.com/open-circle/valibot/commit/1bd…	x_refsource_MISC
https://github.com/open-circle/valibot/releases/t…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
open-circle	valibot	Affected: < 1.4.2

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "valibot",
          "vendor": "open-circle",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.4.2"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Valibot helps validate data using a schema. Versions prior to 1.4.2 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\u0027s 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 returning structured validation errors. This issue has been fixed in version 1.4.2."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 6.9,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "LOW",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-755",
              "description": "CWE-755: Improper Handling of Exceptional Conditions",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-30T00:10:32.598Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/open-circle/valibot/security/advisories/GHSA-5qjj-4xww-7phc",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/open-circle/valibot/security/advisories/GHSA-5qjj-4xww-7phc"
        },
        {
          "name": "https://github.com/open-circle/valibot/pull/1522",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/open-circle/valibot/pull/1522"
        },
        {
          "name": "https://github.com/open-circle/valibot/commit/1bd01c304657cd0809cc92694360b6cc60f700bf",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/open-circle/valibot/commit/1bd01c304657cd0809cc92694360b6cc60f700bf"
        },
        {
          "name": "https://github.com/open-circle/valibot/releases/tag/v1.4.2",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/open-circle/valibot/releases/tag/v1.4.2"
        }
      ],
      "source": {
        "advisory": "GHSA-5qjj-4xww-7phc",
        "discovery": "UNKNOWN"
      },
      "title": "Valibot: record() issue paths can make flatten() throw for inherited Object property names"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-59952",
    "datePublished": "2026-07-30T00:10:32.598Z",
    "dateReserved": "2026-07-07T18:49:15.607Z",
    "dateUpdated": "2026-07-30T00:10:32.598Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

GHSA-5QJJ-4XWW-7PHC

Summary

Affected package

Root cause

Impact

Local reproduction

Duplicate checks performed before submission

Suggested remediation

CVE-2026-59952 (GCVE-0-2026-59952)

Tags

Sightings

Nomenclature