CVE-2026-33994 Locutus Prototype Pollution due to incomplete fix for CVE-2026-25521
Attackers can pollute Object.prototype in the Locutus library by bypassing guards, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33994?
CVE-2026-33994 is a medium-severity vulnerability in locutusjs locutus, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-1321
Which versions are affected by CVE-2026-33994?
2 open source packages ship an affected version, including locutus. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
locutus npm | From 2.0.39 | 3.0.25 |
locutus npm | From 2.0.39 | 3.0.25 |
Products include Locutus Locutus.
How do I fix CVE-2026-33994?
Upgrade locutus to 3.0.25 or later.
Is CVE-2026-33994 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33994 exists.
Other vulnerabilities in locutusjs locutus
- CVE-2026-32304 Locutus: RCE via unsanitized input in create_function()
- CVE-2020-7719 Prototype Pollution
- CVE-2026-25521 Locutus is vulnerable to Prototype Pollution
- CVE-2026-29091 Locutus: Remote Code Execution (RCE) in locutus call_user_func_array due to Code Injection
- CVE-2026-33993 Locutus has Prototype Pollution via __proto__ Key Injection in unserialize()
Sources
Also known as GHSA-vc8f-x9pp-wf5p.