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SandboxjsApplication · Nyariv

CVE-2026-34208

CRITICAL · 10.0 CVSS v3.1 Published 2026-04-06
Fix available
A fix is available. Upgrade to 0.8.36 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
SandboxJS is a JavaScript sandboxing library. Prior to 0.8.36, SandboxJS blocks direct assignment to global objects (for example Math.random = ...), but this protection can be bypassed through an exposed callable constructor path: this.constructor.call(target, attackerObject). Because this.constructor resolves to the internal SandboxGlobal function and Function.prototype.call is allowed, attacker code can write arbitrary properties into host global objects and persist those mutations across sandbox instances in the same process. This vulnerability is fixed in 0.8.36.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

SandboxJS versions prior to 0.8.36 have a sandbox escape vulnerability where the protection against direct assignment to global objects (e.g., Math.random = ...) can be bypassed through a callable constructor path using 'this.constructor.call(target, attackerObject)'. Since this.constructor resolves to the internal SandboxGlobal function and Function.prototype.call is permitted, attackers can write arbitrary properties to host global objects with mutations persisting across all sandbox instances in the same process.

MitigationUpgrade SandboxJS to version 0.8.36 or later to remediate this vulnerability. After upgrading, verify that sandboxed code can no longer mutate host global objects through the constructor.call() bypass.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
SandboxjsApplication
Affected:< 0.8.36

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed SandboxJS version
    Run 'npm list sandboxjs' or check your package.json dependencies to find the installed version of sandboxjs
    Affected if The installed version is below 0.8.36
  2. Locate the sandboxjs package in node_modules
    Find the sandboxjs package directory in your node_modules folder and locate the main entry file
    Affected if Unable to determine version or package not found in expected location
  3. Test the vulnerable constructor.call bypass
    Create a sandbox instance and attempt to execute: 'var s = sandbox(); s.run("this.constructor.call(Math, {random: function(){return 0.5}})")' to see if host Math object can be mutated
    Affected if The constructor.call() path successfully mutates host global objects like Math.random
  4. Verify persistence across sandbox instances
    After the above mutation, create a new sandbox instance and check if the mutation persists: 'var s2 = sandbox(); s2.run("Math.random()")' should return 0.5 if vulnerable
    Affected if Mutations to host globals persist across different sandbox instances in the same process

If SandboxJS version is below 0.8.36 AND the constructor.call() bypass successfully mutates host global objects with mutations persisting across sandbox instances, the environment is affected by this CVE.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.8.36 or later
Fixed in 0.8.36
Interim mitigation

Upgrade SandboxJS to version 0.8.36 or later to remediate this vulnerability. After upgrading, verify that sandboxed code can no longer mutate host global objects through the constructor.call() bypass.

Recommended fix High confidence

sandboxjs version 0.8.36

  1. Check the current version of SandboxJS in your project by inspecting package.json or running npm list sandboxjs
  2. Upgrade SandboxJS to version 0.8.36 or later by running: npm install sandboxjs@^0.8.36 (or npm update sandboxjs)
  3. Verify the installed version is 0.8.36 or higher using npm list sandboxjs
  4. Test your application's sandbox functionality to ensure the upgrade does not break expected behavior
  5. Ensure any automated tests pass, particularly tests that exercise sandbox isolation and global object protection
Caveat Review the SandboxJS changelog between your current version and 0.8.36 for any API changes that may affect your implementation

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Sandboxjs Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,380
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-34208 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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