CVE-2026-84367: joi Object().rename() With A Template Target Vulnerability

LOW
Advisory Identifier: GHSA-gg4h-3hg2-grpc
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CVSS 3.7
CWE-1321
Published
Advisory Summary

CVE-2026-84367 is a LOW (CVSS 3.7) object().rename() with a template target vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting joi libraries in the npm ecosystem. The issue involves object().rename() with a template target can set the validated object's prototype. Remediation is available by upgrading affected packages to version 17.13.5, 18.2.4.

CVE-2026-84367 at a Glance

CVE Identifier CVE-2026-84367
GHSA Identifier GHSA-gg4h-3hg2-grpc
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product joi
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 3.7

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-84367

To remediate this vulnerability, upgrade all affected joi dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

joi fixed: 17.13.5 
npm install joi@17.13.5
joi fixed: 18.2.4 
npm install joi@18.2.4
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls joi

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-84367, inspect your project dependencies using npm:

npm ls joi

Analyze the terminal output to locate any version of joi in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 17.13.5), your application is affected.

Note: The npm ls joi command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. In joi, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Applications are affected only if a schema renames keys with a regular-expression source and a `Joi.expression()` / `Joi.x()` target that interpolates the pattern's own match data, combined with `{ multiple: true }`, for example `.rename(/^x-(.+)$/, Joi.x('{#1}'), { multiple: true })`. Because the target is rendered from the matched input key, an attacker who controls input keys can send `x-__proto__` with an object value and make the rename target render as `__proto__`, which sets the prototype of the object joi returns instead of creating a key on it. The global `Object.prototype` is not modified, so the effect is confined to the object returned by that one `validate()` call. Schemas using a static string rename target are not affected, and neither are schemas left on the default `{ multiple: false }`. ### Patches Versions 17.13.5 and 18.2.4 have been released to address the issue. ### Workarounds 1. Replace the template rename target with a static string target. 2. Keep the template but make the capture unable to produce `__proto__`, using a negative lookahead: `.rename(/^x-(?!__proto__$)(.+)$/, Joi.x('{#1}'), { multiple: true })` 3. Drop { multiple: true } from the rename, which stops the rename before the assignment.

CVE-2026-84367 Affected joi Versions

2 component(s)
Fixed Versions:
17.13.518.2.4
Product / Package Ecosystem Affected Versions Fixed Version
joi
npm/joi
npm
≥ 16.0.0
< 17.13.5
17.13.5
joi
npm/joi
npm
≥ 18.0.0
< 18.2.4
18.2.4

References

GitHub Advisory / Wiki ADVISORY
https://github.com/hapijs/joi/security/advisories/GHSA-gg4h-3hg2-grpc
NVD — CVE-2026-84367 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84367
joi Source Repository REPOSITORY
https://github.com/hapijs/joi/pull/3134
joi Source Repository REPOSITORY
https://github.com/hapijs/joi/pull/3135
Security Fix Commit FIX COMMIT
https://github.com/hapijs/joi/commit/162f367aa178d2e1ebec8dc1164e5fe16536ddf6
Security Fix Commit FIX COMMIT
https://github.com/hapijs/joi/commit/172ececa192feda532b743d77bc9d3e523d19b01
joi Source Repository REPOSITORY
https://github.com/hapijs/joi
joi Release RELEASE
https://github.com/hapijs/joi/releases/tag/v17.13.5
joi Release RELEASE
https://github.com/hapijs/joi/releases/tag/v18.2.4

Frequently Asked Questions

What is CVE-2026-84367?
CVE-2026-84367 is a security vulnerability in joi involving object().rename() with a template target can set the validated object's prototype under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which joi versions are affected?
Affected versions include releases prior to 17.13.5, 18.2.4 across affected packages: joi.
What version fixes CVE-2026-84367?
Upgrading to 17.13.5, 18.2.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is joi affected?
Yes, joi is affected in releases prior to 17.13.5, 18.2.4. Upgrade your dependency to 17.13.5, 18.2.4 or later.
What is the CVSS score of CVE-2026-84367?
CVE-2026-84367 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-84367?
CVE-2026-84367 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check npm dependencies for CVE-2026-84367?
Run the dependency tree command: 'npm ls joi'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gg4h-3hg2-grpc",
  "modified" : "2026-09-08T20:51:21Z",
  "published" : "2026-09-08T20:51:21Z",
  "aliases" : [ "CVE-2026-84367" ],
  "summary" : "joi: object().rename() with a template target can set the validated object's prototype",
  "details" : "### Impact\n\nApplications are affected only if a schema renames keys with a regular-expression source and a `Joi.expression()` / `Joi.x()` target that interpolates the pattern's own match data, combined with `{ multiple: true }`, for example `.rename(/^x-(.+)$/, Joi.x('{#1}'), { multiple: true })`. Because the target is rendered from the matched input key, an attacker who controls input keys can send `x-__proto__` with an object value and make the rename target render as `__proto__`, which sets the prototype of the object joi returns instead of creating a key on it. The global `Object.prototype` is not modified, so the effect is confined to the object returned by that one `validate()` call.\n\nSchemas using a static string rename target are not affected, and neither are schemas left on the default `{ multiple: false }`.\n\n### Patches\n\nVersions 17.13.5 and 18.2.4 have been released to address the issue.\n\n### Workarounds\n\n1. Replace the template rename target with a static string target.\n2. Keep the template but make the capture unable to produce `__proto__`, using a negative lookahead: `.rename(/^x-(?!__proto__$)(.+)$/, Joi.x('{#1}'), { multiple: true })`\n3. Drop { multiple: true } from the rename, which stops the rename before the assignment.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "joi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "16.0.0"
      }, {
        "fixed" : "17.13.5"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "joi"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "18.0.0"
      }, {
        "fixed" : "18.2.4"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/security/advisories/GHSA-gg4h-3hg2-grpc"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84367"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/pull/3134"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/pull/3135"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/commit/162f367aa178d2e1ebec8dc1164e5fe16536ddf6"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/commit/172ececa192feda532b743d77bc9d3e523d19b01"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/hapijs/joi"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/releases/tag/v17.13.5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/hapijs/joi/releases/tag/v18.2.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T20:51:21Z",
    "nvd_published_at" : "2026-09-01T21:18:47Z"
  }
}