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

> Attackers can escape the SandboxJS sandbox by exploiting a time-of-check time-of-use race condition in property key validation, 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-7x3h-rm86-3342

## What is CVE-2026-25641?

CVE-2026-25641 is a critical 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, 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.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-25641?

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-2026-25641?

Upgrade @nyariv/sandboxjs to 0.8.29 or later.

## Is CVE-2026-25641 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25641 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-2026-25641 and fix it if it is affected.

What it is: CVE-2026-25641 is a critical 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-2026-25641 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-2026-25641/ (Markdown: https://insights.sbomify.com/CVE-2026-25641/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-25641
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-25641
- OSV: https://osv.dev/vulnerability/CVE-2026-25641

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-25641/
Summaries are generated and may contain mistakes; the official description above is the record.