---
title: "CVE-2026-43898: SandboxJS has a sandbox escape via Function.caller leakage of internal call op"
url: https://erroneo.us/security/cve/CVE-2026-43898/
description: "CVE-2026-43898 (@nyariv/sandboxjs (npm)): SandboxJS is a JavaScript sandboxing library. Prior to 0.9.6, sandbox-defined functions expose Function.caller…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-28
date_modified: 2026-06-09
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-43898"
kev: false
cvss: 10
epss: 0.00632
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-43898: SandboxJS has a sandbox escape via Function.caller leakage of internal call op

**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 50: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 50% 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) <= 0.9.5, fixed in 0.9.6 . Check your lockfile, including transitive dependencies.

## What it is

SandboxJS is a JavaScript sandboxing library. Prior to 0.9.6, sandbox-defined functions expose Function.caller, allowing sandboxed code to recover the internal LispType.Call runtime callback. That callback can then be invoked with attacker-controlled fake context and obj values to extract blocked host statics, recover the real host Function constructor, and execute arbitrary host JavaScript. This vulnerability is fixed in 0.9.6.

## Affected packages

- npm `@nyariv/sandboxjs` <= 0.9.5 → fixed: 0.9.6

## Affected products (CVE record)

- nyariv SandboxJS: < 0.9.6

## 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): 0.63% probability of exploitation activity in the next 30 days; percentile 50.

## Sources

- [GitHub Advisory GHSA-g8f2-4f4f-5jqw](https://github.com/advisories/GHSA-g8f2-4f4f-5jqw)
- [CVE.org record CVE-2026-43898](https://www.cve.org/CVERecord?id=CVE-2026-43898)
- [NVD entry CVE-2026-43898](https://nvd.nist.gov/vuln/detail/CVE-2026-43898)
- [github.com](https://github.com/nyariv/SandboxJS/security/advisories/GHSA-g8f2-4f4f-5jqw)
- [github.com](https://github.com/nyariv/SandboxJS/commit/826865251232611ec94078bab5a18ec875dad4a5)

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Source page: https://erroneo.us/security/cve/CVE-2026-43898/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt