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GHSA-6W3J-5FW6-R9VR

Vulnerability from github – Published: 2026-09-08 20:55 – Updated: 2026-09-08 20:55
VLAI
Summary
joi: Prototype pollution via a `__proto__` language key in custom messages
Details

Impact

An application that passes attacker-controlled data into joi's custom message configuration (messages(), message(), prefs({ messages }), Joi.extend({ messages }) or rule({ message })) lets the attacker write properties onto Object.prototype, where every object in the process then inherits them. A key named __proto__ was treated as a language name, and the code reused the object it found at that key, which resolves to the prototype rather than to a new own property; a key named constructor did the same to the Object function's statics. A consuming application that gates on the mere presence of a property (if (user.isAdmin)) can be made to take the wrong branch for every object it inspects.

This is not reachable from data that joi validates. Custom messages are schema-construction configuration, normally written by the application developer. Exploitation therefore requires an application that feeds untrusted input straight into schema construction.

Patches

Upgrade to version 18.2.5 or 17.13.6.

Workarounds

Do not pass untrusted input into messages(), message(), prefs({ messages }), Joi.extend({ messages }) or rule({ message }). Or validate that they don't contain any __proto__ or constructor property.

Severity
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "joi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "17.2.0"
            },
            {
              "fixed": "17.13.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "@hapi/joi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "16.0.0"
            },
            {
              "last_affected": "17.1.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "joi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "18.0.0"
            },
            {
              "fixed": "18.2.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-84368"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-08T20:55:58Z",
    "nvd_published_at": "2026-09-01T21:18:47Z",
    "severity": "LOW"
  },
  "details": "### Impact\nAn application that passes attacker-controlled data into joi\u0027s custom message configuration (`messages()`, `message()`, `prefs({ messages })`, `Joi.extend({ messages })` or `rule({ message })`) lets the attacker write properties onto `Object.prototype`, where every object in the process then inherits them. A key named `__proto__` was treated as a language name, and the code reused the object it found at that key, which resolves to the prototype rather than to a new own property; a key named `constructor` did the same to the `Object` function\u0027s statics. A consuming application that gates on the mere presence of a property (`if (user.isAdmin)`) can be made to take the wrong branch for every object it inspects.\n\nThis is not reachable from data that joi validates. Custom messages are schema-construction configuration, normally written by the application developer. Exploitation therefore requires an application that feeds untrusted input straight into schema construction.\n\n### Patches\nUpgrade to version 18.2.5 or 17.13.6.\n\n### Workarounds\nDo not pass untrusted input into `messages()`, `message()`, `prefs({ messages })`, `Joi.extend({ messages })` or `rule({ message })`. Or validate that they don\u0027t contain any `__proto__` or `constructor` property.",
  "id": "GHSA-6w3j-5fw6-r9vr",
  "modified": "2026-09-08T20:55:58Z",
  "published": "2026-09-08T20:55:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/hapijs/joi/security/advisories/GHSA-6w3j-5fw6-r9vr"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-84368"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapijs/joi/pull/3138"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapijs/joi/pull/3139"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapijs/joi/commit/8d0b808f3e874d28f9078f61b7742290989afb36"
    },
    {
      "type": "WEB",
      "url": "https://github.com/hapijs/joi/commit/90d07571923c90e3432a328fc041d1cda03d30fa"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/hapijs/joi"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "joi: Prototype pollution via a `__proto__` language key in custom messages"
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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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.
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  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
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  • 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.