CVE-2026-25521: Locutus Locutus Is Vulnerable To Prototype Vulnerability

CRITICAL
Advisory Identifier: GHSA-rxrv-835q-v5mh
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CWE-1321 CWE-915
Published
Advisory Summary

CVE-2026-25521 is a CRITICAL locutus is vulnerable to prototype vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting Locutus libraries in the npm ecosystem. The issue involves locutus is vulnerable to prototype pollution. Remediation is available by upgrading affected packages to version 2.0.39.

CVE-2026-25521 at a Glance

CVE Identifier CVE-2026-25521
GHSA Identifier GHSA-rxrv-835q-v5mh
Severity CRITICAL
CVSS v3.1 Base Score N/A
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product Locutus
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-25521

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

locutus fixed: 2.0.39 
npm install locutus@2.0.39
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 locutus

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-25521, inspect your project dependencies using npm:

npm ls locutus

Analyze the terminal output to locate any version of Locutus in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.0.39), your application is affected.

Note: The npm ls locutus 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 Locutus, 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

### Summary A Prototype Pollution vulnerability exists in the the npm package locutus (>2.0.12). Despite a previous fix that attempted to mitigate Prototype Pollution by checking whether user input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using String.prototype. This issue was fixed in version 2.0.39. ### Details The vulnerability resides in line 77 to 79 of https://github.com/locutusjs/locutus/blob/main/src/php/strings/parse_str.js where includes() function is used to check whether user provided input contain forbidden strings. ### PoC #### Steps to reproduce 1. Install latest version of locutus using npm install or cloning from git 2. Run the following code snippet: ```javascript String.prototype.includes = () => false; console.log({}.polluted); const locutus = require('locutus'); locutus.php.strings.parse_str('constructor[prototype][polluted]=yes'); console.log({}.polluted); // prints yes -> indicating that the patch was bypassed and Prototype Pollution occurred ``` #### Expected behavior Prototype Pollution should be prevented and {} should not gain new properties. This should be printed on the console: ``` undefined undefined OR throw an Error ``` #### Actual behavior Object.prototype is polluted This is printed on the console: ``` undefined yes ``` ### Impact This is a Prototype Pollution vulnerability, which can have severe security implications depending on how locutus is used by downstream applications. Any application that processes attacker-controlled input using this `locutus.php.strings.parse_str` may be affected. It could potentially lead to the following problems: 1. Authentication bypass 2. Denial of service 3. Remote code execution (if polluted property is passed to sinks like eval or child_process)

CVE-2026-25521 Affected Locutus Versions

1 component(s)
Fixed Versions:
2.0.39
Product / Package Ecosystem Affected Versions Fixed Version
locutus
npm/locutus
npm
≥ 2.0.12
< 2.0.39
2.0.39

References

GitHub Advisory / Wiki ADVISORY
https://github.com/locutusjs/locutus/security/advisories/GHSA-rxrv-835q-v5mh
NVD — CVE-2026-25521 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-25521
Security Fix Commit FIX COMMIT
https://github.com/locutusjs/locutus/commit/042af9ca7fde2ff599120783e720a17f335bb01c
Locutus Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-25521
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2436950
Locutus Source Repository REPOSITORY
https://github.com/locutusjs/locutus
Locutus Security Information SECURITY
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-25521.json

Frequently Asked Questions

What is CVE-2026-25521?
CVE-2026-25521 is a security vulnerability in Locutus involving locutus is vulnerable to Prototype Pollution under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which Locutus versions are affected?
Affected versions include releases prior to 2.0.39 across affected packages: locutus.
What version fixes CVE-2026-25521?
Upgrading to 2.0.39 (or the latest patched release for your respective branch) resolves the vulnerability.
Is locutus affected?
Yes, locutus is affected in releases prior to 2.0.39. Upgrade your dependency to 2.0.39 or later.
What CWE is associated with CVE-2026-25521?
CVE-2026-25521 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-2026-25521?
Run the dependency tree command: 'npm ls locutus'. 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-rxrv-835q-v5mh",
  "modified" : "2026-10-05T15:34:16Z",
  "published" : "2026-02-02T22:21:54Z",
  "aliases" : [ "CVE-2026-25521" ],
  "summary" : "locutus is vulnerable to Prototype Pollution",
  "details" : "### Summary\nA Prototype Pollution vulnerability exists in the the npm package locutus (>2.0.12). Despite a previous fix that attempted to mitigate Prototype Pollution by checking whether user input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using String.prototype. This issue was fixed in version 2.0.39.\n\n### Details\nThe vulnerability resides in line 77 to 79 of https://github.com/locutusjs/locutus/blob/main/src/php/strings/parse_str.js where includes() function is used to check whether user provided input contain forbidden strings.\n\n### PoC\n\n#### Steps to reproduce\n1. Install latest version of locutus using npm install or cloning from git\n2. Run the following code snippet:\n\n```javascript\nString.prototype.includes = () => false;      \nconsole.log({}.polluted);\nconst locutus = require('locutus');\nlocutus.php.strings.parse_str('constructor[prototype][polluted]=yes');\nconsole.log({}.polluted);  // prints yes -> indicating that the patch was bypassed and Prototype Pollution occurred\n```\n\n#### Expected behavior\nPrototype Pollution should be prevented and {} should not gain new properties.\nThis should be printed on the console:\n```\nundefined\nundefined OR throw an Error\n```\n\n#### Actual behavior\nObject.prototype is polluted\nThis is printed on the console:\n```\nundefined \nyes\n```\n\n### Impact\nThis is a Prototype Pollution vulnerability, which can have severe security implications depending on how locutus is used by downstream applications. Any application that processes attacker-controlled input using this `locutus.php.strings.parse_str` may be affected. It could potentially lead to the following problems:\n1. Authentication bypass\n2. Denial of service\n3. Remote code execution (if polluted property is passed to sinks like eval or child_process)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "locutus"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.0.12"
      }, {
        "fixed" : "2.0.39"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/locutusjs/locutus/security/advisories/GHSA-rxrv-835q-v5mh"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-25521"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/locutusjs/locutus/commit/042af9ca7fde2ff599120783e720a17f335bb01c"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/security/cve/CVE-2026-25521"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2436950"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/locutusjs/locutus"
  }, {
    "type" : "WEB",
    "url" : "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-25521.json"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1321", "CWE-915" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-02T22:21:54Z",
    "nvd_published_at" : "2026-02-04T22:15:59Z"
  }
}