# CVE-2026-25587: SandboxJS has a Sandbox Escape

> Attackers can escape the SandboxJS sandbox by overwriting Map.prototype.has, leading to arbitrary code execution.

- **Severity:** Critical 10.0 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Feb 2026
- **Updated:** 6 Feb 2026
- **Also known as:** GHSA-66h4-qj4x-38xp

## What is CVE-2026-25587?

CVE-2026-25587 is a critical code injection vulnerability in nyariv SandboxJS, published on 6 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, as Map is in SAFE_PROTOYPES, it's prototype can be obtained via Map.prototype. By overwriting Map.prototype.has the sandbox can be escaped. This vulnerability is fixed in 0.8.29.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-25587?

2 open source packages ship an affected version, including @nyariv/sandboxjs. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@nyariv/sandboxjs` | npm | All versions | 0.8.29 |
| `@nyariv/sandboxjs` | npm | All versions | 0.8.29 |

Products: Nyariv Sandboxjs.

## How do I fix CVE-2026-25587?

Upgrade @nyariv/sandboxjs to 0.8.29 or later.

## Is CVE-2026-25587 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25587 exists.

## Other vulnerabilities in nyariv SandboxJS

- [CVE-2026-43898](https://insights.sbomify.com/CVE-2026-43898/): SandboxJS: Sandbox escape via Function.caller leakage of internal call op (critical 10.0)
- [CVE-2026-34208](https://insights.sbomify.com/CVE-2026-34208/): SandboxJS: Sandbox integrity escape (critical 10.0)
- [CVE-2026-26954](https://insights.sbomify.com/CVE-2026-26954/): SandboxJS has a Sandbox Escape (critical 10.0)
- [CVE-2026-25520](https://insights.sbomify.com/CVE-2026-25520/): SandboxJS has a Sandbox Escape (critical 10.0)
- [CVE-2026-25586](https://insights.sbomify.com/CVE-2026-25586/): SandboxJS has a Sandbox Escape via Prototype Whitelist Bypass and Host Prototype Pollution (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-25587 and fix it if it is affected.

What it is: CVE-2026-25587 is a critical code injection vulnerability in nyariv SandboxJS, published on 6 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25587 exists.

Affected packages and fixed versions:
- @nyariv/sandboxjs (npm): affected all versions; fixed in 0.8.29
- @nyariv/sandboxjs (npm): affected all versions; fixed in 0.8.29

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-2026-25587/ (Markdown: https://insights.sbomify.com/CVE-2026-25587/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25587
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25587
- OSV: https://osv.dev/vulnerability/CVE-2026-25587

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25587/
Summaries are generated and may contain mistakes; the official description above is the record.