CVE-2026-25521
Unknown Unknown - Not Provided
Prototype Pollution in Locutus stdlibs Enables Object Prototype Manipulation

Publication date: 2026-02-04

Last updated on: 2026-02-20

Assigner: GitHub, Inc.

Description
Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. In versions from 2.0.12 to before 2.0.39, a prototype pollution vulnerability exists in locutus. 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 has been patched in version 2.0.39.
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Meta Information
Published
2026-02-04
Last Modified
2026-02-20
Generated
2026-06-16
AI Q&A
2026-02-05
EPSS Evaluated
2026-06-15
NVD
CVE-2026-25521
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
locutus locutus From 2.0.12 (inc) to 2.0.39 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-1321 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.
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Executive Summary

This vulnerability is a prototype pollution issue in the Locutus library, which provides standard libraries of other programming languages for JavaScript. In versions from 2.0.12 up to but not including 2.0.39, an attacker can manipulate the Object.prototype by crafting a malicious input that exploits String.prototype, bypassing previous mitigation attempts that checked for forbidden keys.

Impact Analysis

The vulnerability allows an attacker to pollute the Object.prototype, which can lead to unexpected behavior in JavaScript applications using the affected Locutus versions. This can result in security issues such as privilege escalation, denial of service, or arbitrary code execution depending on how the polluted prototype is used within the application.

Compliance Impact

I don't know

Detection Guidance

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade Locutus to version 2.0.39 or later, where the prototype pollution issue has been patched.

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