@nyariv/sandboxjs has Sandbox Escape via Prototype Whitelist Bypass and Host Prototype Pollution

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

10.0 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS

• CVE-2026-25586: 0.69% estimated exploitation activity in the next 30 days; percentile 52.91 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. The issue was reproducible on Node v23.9.0 using the project’s current build output. The bypass works with default Sandbox configuration and does not require custom globals or whitelists. Root Cause prototypeAccess uses a.hasOwnProperty(b) directly, which can be attacker‑controlled if the sandboxed object shadows hasOwnProperty. When this returns true, the whitelist checks are skipped. - src/executor.ts:348 const prototypeAccess = isFunction || !(a.hasOwnProperty(b) || typeof b === 'number'); <img width="1030" height="593" alt="image" src="https://github.com/user-attachments/assets/0fa0807e-81cc-45b5-be13-bd839c974a4f" / - src/executor.ts:367-399 prototype whitelist…

Published by the source

5 Feb 2026, 21:04 UTC

Last modified by the source

6 Feb 2026, 22:20 UTC

Source last checked

26 Oct 2026, 12:42 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jjpw-65fv-8g48

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-jjpw-65fv-8g48

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-jjpw-65fv-8g48

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-25586

Advisory: @nyariv/sandboxjs has Sandbox Escape via Prototype Whitelist Bypass and Host Prototype Pollution
IDs: CVE-2026-25586, GHSA-jjpw-65fv-8g48
Record: https://patchnext.com/advisories/cve-2026-25586 (revision 3, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 10.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @nyariv/sandboxjs 0.8.29. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @nyariv/sandboxjs: affected <= 0.8.28; fixed in 0.8.29

## Suggested inspection (read-only)
- `npm ls @nyariv/sandboxjs --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @nyariv/sandboxjs.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-jjpw-65fv-8g48 (GitHub-reviewed advisory GHSA-jjpw-65fv-8g48 lists affected ranges: npm @nyariv/sandboxjs >=0 <=0.8.28)
- Verified: https://osv.dev/vulnerability/GHSA-jjpw-65fv-8g48 (OSV record GHSA-jjpw-65fv-8g48 lists affected ranges: npm @nyariv/sandboxjs >=0 <0.8.29 (fixed))

Commands are suggestions: review each one before running it.