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Vulnerability record · CVE-2026-33994 · published 27 March 2026

CVE-2026-33994: Locutus prototype pollution vulnerability

Locutus · Locutus

Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. Starting in version 2.0.39 and prior to version 3.0.25, a prototype pollution vulnerability exists in the `parse_str` function of the npm package locutus. An attacker can pollute `Object.prototype` by overriding `RegExp.prototype.test` and then passing a crafted query string to `parse_str`, bypassing the prototype pollution guard. This vulnerability stems from an incomplete fix for CVE-2026-25521. The CVE-2026-25521 patch replaced the `String.prototype.includes()`-based guard with a `RegExp.prototype.test()`-based guard. However, `RegExp.prototype.test` is itself a writable prototype method that can be overridden, making the new guard bypassable in the same way as the original — trading one hijackable built-in for another. Version 3.0.25 contains an updated fix.

6.3 CVSS 4.0 Medium EPSS 0.76% · top 46.7% CWE-1321 · Prototype pollution
6.3CVSS 4.0 base score
0.76%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
11References, 8 tagged exploit
17 Jun 2026Last modified by NVD

Description

Locutus brings stdlibs of other programming languages to JavaScript for educational purposes. Starting in version 2.0.39 and prior to version 3.0.25, a prototype pollution vulnerability exists in the `parse_str` function of the npm package locutus. An attacker can pollute `Object.prototype` by overriding `RegExp.prototype.test` and then passing a crafted query string to `parse_str`, bypassing the prototype pollution guard. This vulnerability stems from an incomplete fix for CVE-2026-25521. The CVE-2026-25521 patch replaced the `String.prototype.includes()`-based guard with a `RegExp.prototype.test()`-based guard. However, `RegExp.prototype.test` is itself a writable prototype method that can be overridden, making the new guard bypassable in the same way as the original — trading one hijackable built-in for another. Version 3.0.25 contains an updated fix.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4 Patch
https://github.com/locutusjs/locutus/pull/597 Issue Tracking
https://github.com/locutusjs/locutus/releases/tag/v3.0.25 Release Notes
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory
https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-33994), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.