CVE-2026-33994
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.
Does this matter?
Lower severity and a low EPSS score (0.56%). Track it; it rarely justifies an emergency change on its own.
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
- 6.3 MEDIUMCVSS: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/M
- EPSS
- 0.56% probability · 45th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1321
- Affected
- locutus/locutus
- Source
- security-advisories@github.com
References
- https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4Patch
- https://github.com/locutusjs/locutus/pull/597Issue Tracking
- https://github.com/locutusjs/locutus/releases/tag/v3.0.25Release Notes
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5pExploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.