---
title: "CVE-2026-25641: @nyariv/sandboxjs vulnerable to sandbox escape via TOCTOU bug on keys in property accesses"
url: https://erroneo.us/security/cve/CVE-2026-25641/
description: "CVE-2026-25641 (@nyariv/sandboxjs (npm)): SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, there is a sandbox escape vulnerability due to a…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-02-06
date_modified: 2026-02-06
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-25641"
kev: false
cvss: 10
epss: 0.00576
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-25641: @nyariv/sandboxjs vulnerable to sandbox escape via TOCTOU bug on keys in property accesses

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.6% , percentile 47: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 47% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes @nyariv/sandboxjs (npm) <= 0.8.28, fixed in 0.8.29 . Check your lockfile, including transitive dependencies.

## What it is

SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, there is a sandbox escape vulnerability due to a mismatch between the key on which the validation is performed and the key used for accessing properties. Even though the key used in property accesses is annotated as string, this is never enforced. So, attackers can pass malicious objects that coerce to different string values when used, e.g., one for the time the key is sanitized using hasOwnProperty(key) and a different one for when the key is used for the actual property access. This vulnerability is fixed in 0.8.29.

## Affected packages

- npm `@nyariv/sandboxjs` <= 0.8.28 → fixed: 0.8.29

## Affected products (CVE record)

- nyariv SandboxJS: < 0.8.29

## Severity

- GitHub_M CVSS 3.1: 10 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`
- GitHub CVSS 3.1: 10.0 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.58% probability of exploitation activity in the next 30 days; percentile 47.

## Sources

- [GitHub Advisory GHSA-7x3h-rm86-3342](https://github.com/advisories/GHSA-7x3h-rm86-3342)
- [CVE.org record CVE-2026-25641](https://www.cve.org/CVERecord?id=CVE-2026-25641)
- [NVD entry CVE-2026-25641](https://nvd.nist.gov/vuln/detail/CVE-2026-25641)
- [github.com](https://github.com/nyariv/SandboxJS/security/advisories/GHSA-7x3h-rm86-3342)
- [github.com](https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3)
- [github.com](https://github.com/nyariv/SandboxJS/blob/6103d7147c4666fe48cfda58a4d5f37005b43754/src/executor.ts#L304-L304)

---
Source page: https://erroneo.us/security/cve/CVE-2026-25641/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt