SandboxJS has a sandbox escape via Function.caller leakage of internal call op

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

10.0 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS

• CVE-2026-43898: 0.47% estimated exploitation activity in the next 30 days; percentile 40.88 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details The vulnerability is in the property access logic registered via addOps in prop.ts. Sandboxed code could access the caller, callee, and arguments properties on functions. In the CommonJS build, this allowed sandboxed code to read Function.caller and leak a privileged internal LispType.Call callback. In executorUtils.ts createFunction() constructs normal host JS functions, and because these are ordinary host functions, sandbox code can observe: That leaks the host-side callback that invoked the sandbox function. This leaked callback is the internal LispType.Call op, which is registered in call.ts. The escape was possible because the…

Published by the source

11 May 2026, 19:40 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 12:53 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-g8f2-4f4f-5jqw

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-g8f2-4f4f-5jqw

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-g8f2-4f4f-5jqw

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# Patch Next advisory brief: CVE-2026-43898

Advisory: SandboxJS has a sandbox escape via Function.caller leakage of internal call op
IDs: CVE-2026-43898, GHSA-g8f2-4f4f-5jqw
Record: https://patchnext.com/advisories/cve-2026-43898 (revision 3, source checked 26 Oct 2026, 12:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 10.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @nyariv/sandboxjs 0.9.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @nyariv/sandboxjs: affected <= 0.9.5; fixed in 0.9.6

## Suggested inspection (read-only)
- `npm ls @nyariv/sandboxjs --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @nyariv/sandboxjs.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-g8f2-4f4f-5jqw (GitHub-reviewed advisory GHSA-g8f2-4f4f-5jqw lists affected ranges: npm @nyariv/sandboxjs >=0 <=0.9.5)
- Verified: https://osv.dev/vulnerability/GHSA-g8f2-4f4f-5jqw (OSV record GHSA-g8f2-4f4f-5jqw lists affected ranges: npm @nyariv/sandboxjs >=0 <0.9.6 (fixed))

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