# CVE-2026-25521: Locutus is vulnerable to Prototype Pollution

> Attackers can pollute Object.prototype via crafted input, potentially leading to code execution or privilege escalation in applications using the Locutus library.

- **Severity:** Critical 9.4 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Feb 2026
- **Updated:** 15 Jul 2026
- **Also known as:** GHSA-rxrv-835q-v5mh

## What is CVE-2026-25521?

CVE-2026-25521 is a critical vulnerability in locutusjs locutus, published on 4 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-915 (Improperly Controlled Modification of Dynamically-Determined Object Attributes), CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-25521?

2 open source packages ship an affected version, including locutus. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `locutus` | npm | From 2.0.12 | 2.0.39 |
| `locutus` | npm | From 2.0.12 | 2.0.39 |

Products: Locutus Locutus.

## How do I fix CVE-2026-25521?

Upgrade locutus to 2.0.39 or later.

## Is CVE-2026-25521 being exploited?

There is no known exploitation of CVE-2026-25521 in the wild and no public exploit code.

## Other vulnerabilities in locutusjs locutus

- [CVE-2026-32304](https://insights.sbomify.com/CVE-2026-32304/): Locutus: RCE via unsanitized input in create_function() (critical 9.8)
- [CVE-2020-7719](https://insights.sbomify.com/CVE-2020-7719/): Prototype Pollution (critical 9.8)
- [CVE-2026-29091](https://insights.sbomify.com/CVE-2026-29091/): Locutus: Remote Code Execution (RCE) in locutus call_user_func_array due to Code Injection (high 8.1)
- [CVE-2026-33993](https://insights.sbomify.com/CVE-2026-33993/): Locutus has Prototype Pollution via __proto__ Key Injection in unserialize() (medium 6.9)
- [CVE-2026-33994](https://insights.sbomify.com/CVE-2026-33994/): Locutus Prototype Pollution due to incomplete fix for CVE-2026-25521 (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25521 and fix it if it is affected.

What it is: CVE-2026-25521 is a critical vulnerability in locutusjs locutus, published on 4 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-25521 in the wild and no public exploit code.

Affected packages and fixed versions:
- locutus (npm): affected from 2.0.12; fixed in 2.0.39
- locutus (npm): affected from 2.0.12; fixed in 2.0.39

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-25521/ (Markdown: https://insights.sbomify.com/CVE-2026-25521/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25521
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25521
- OSV: https://osv.dev/vulnerability/CVE-2026-25521

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25521/
Summaries are generated and may contain mistakes; the official description above is the record.