# CVE-2026-43898: nyariv SandboxJS sandbox escape via Function.caller leakage

Source: https://junglewise.ai/threats/cve-2026-43898-nyariv-sandboxjs-sandbox-escape-via-function-caller-leakage  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-28. Updated: 2026-06-09  
License: CC BY 4.0 with a link back

CVE-2026-43898 · Severity: critical · CVSS 10 · Published 2026-05-28

SandboxJS is a library used to execute untrusted JavaScript code in a restricted environment. A vulnerability allows an attacker to bypass these restrictions and execute arbitrary commands on the underlying server or host system. This could lead to full system compromise, unauthorized data access, or complete service disruption.

Technologies: [@nyariv/sandboxjs (npm)](https://junglewise.ai/threats/technologies/nyariv-sandboxjs), [Nyariv Sandboxjs](https://junglewise.ai/threats/technologies/sandboxjs). Vendors: [npm](https://junglewise.ai/threats/vendors/npm), [Nyariv](https://junglewise.ai/threats/vendors/nyariv).

## Quick answers

**Is CVE-2026-43898 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-43898 being exploited in the wild.

**How severe is CVE-2026-43898?** Critical severity, with a CVSS score of 10, published 28 May 2026.

**Which products and versions are affected?** @nyariv/sandboxjs (npm) <= 0.9.5, SEMVER:introduced=0,fixed=0.9.6; Nyariv Sandboxjs < 0.9.6, <= 0.9.5.

**Is there a fix for CVE-2026-43898?** Yes. @nyariv/sandboxjs (npm): upgrade to 0.9.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-43898 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-43898?** Check whether you run @nyariv/sandboxjs (npm) or Nyariv Sandboxjs at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- @nyariv/sandboxjs (npm): upgrade to 0.9.6 or later

  ```sh
  npm install @nyariv/sandboxjs@0.9.6
  ```


## Technical details

A sandbox escape exists in SandboxJS due to the exposure of 'Function.caller' in sandboxed functions, particularly in CommonJS builds. This allows sandboxed code to leak the internal 'LispType.Call' runtime callback. Because the 'LispType.Call' handler in 'call.ts' fails to authenticate the 'params' object, an attacker can invoke it with forged operands. This enables the extraction of blocked host statics and the recovery of the host's Function constructor, leading to arbitrary JavaScript execution in the host context. The issue is patched in version 0.9.6.

## Affected products

- nyariv @nyariv/sandboxjs <= 0.9.5

## Identifiers

- CVE-2026-43898
- GHSA-g8f2-4f4f-5jqw

## Timeline

- 2026-05-09: disclosed
- 2026-05-11: advisory
- 2026-05-11: patched: Version 0.9.6 released

## References

- [https://api.github.com/users/Macabely](https://api.github.com/users/Macabely)
- [https://github.com/Macabely](https://github.com/Macabely)
- [https://api.github.com/users/Macabely/gists%7B/gist_id%7D](https://api.github.com/users/Macabely/gists%7B/gist_id%7D)
- [https://api.github.com/users/Macabely/repos](https://api.github.com/users/Macabely/repos)
- [https://avatars.githubusercontent.com/u/172206083?v=4](https://avatars.githubusercontent.com/u/172206083?v=4)
- [https://api.github.com/users/Macabely/events%7B/privacy%7D](https://api.github.com/users/Macabely/events%7B/privacy%7D)

## Related threats

- [SandboxJS sandbox escape via Prop object leak in new handler](https://junglewise.ai/threats/cve-2026-34217-sandboxjs-sandbox-escape-via-prop-object-leak-in-new-handler)
- [SandboxJS stack overflow via deeply nested expressions](https://junglewise.ai/threats/cve-2026-34211-sandboxjs-stack-overflow-via-deeply-nested-expressions)
- [SandboxJS sandbox integrity escape via constructor manipulation](https://junglewise.ai/threats/cve-2026-34208-nyariv-sandboxjs-sandbox-integrity-escape-via-constructor-bypass)
- [SandboxJS execution-quota bypass in timers](https://junglewise.ai/threats/cve-2026-32723-sandboxjs-execution-quota-bypass-in-timers)
- [SandboxJS sandbox escape allowing remote code execution](https://junglewise.ai/threats/cve-2026-26954-sandboxjs-sandbox-escape-allowing-remote-code-execution)