CVE-2026-34217: Nyariv Sandboxjs Information Disclosure

CVE-2026-34217 Overview

CVE-2026-34217 is a scope modification vulnerability in @nyariv/sandboxjs, a JavaScript sandboxing library used to execute untrusted code in isolated environments. Prior to version 0.8.36, a flaw in the sandbox implementation allows untrusted sandboxed code to leak internal interpreter objects through the new operator. This exposes sandbox scope objects in the scope hierarchy to untrusted code, creating an unexpected and undesired exploit vector.

While this vulnerability allows modification of scopes inside the sandbox, it's important to note that code evaluation remains sandboxed and prototypes remain protected throughout execution. However, the exposure of internal scope objects represents a significant weakening of the sandbox's security boundaries.

Critical Impact

Untrusted sandboxed code can access and modify internal interpreter scope objects, potentially compromising the isolation guarantees that sandboxing libraries are designed to provide.

Affected Products

• nyariv sandboxjs versions prior to 0.8.36
• Applications using @nyariv/sandboxjs for Node.js sandboxing
• Web applications relying on SandboxJS for client-side code isolation

Discovery Timeline

• 2026-04-06 - CVE-2026-34217 published to NVD
• 2026-04-09 - Last updated in NVD database

Technical Details for CVE-2026-34217

Vulnerability Analysis

This vulnerability falls under CWE-668 (Exposure of Resource to Wrong Sphere), which occurs when a product exposes a resource to the wrong control sphere, providing unintended actors with inappropriate access to the resource.

In the context of SandboxJS, the JavaScript sandboxing mechanism is designed to create an isolated execution environment where untrusted code can run without accessing the host application's scope or sensitive objects. The vulnerability undermines this isolation by allowing sandboxed code to leverage the new operator to access internal interpreter objects that should remain hidden.

The scope modification flaw enables attackers running code within the sandbox to traverse the scope hierarchy and access objects that were not intended to be exposed. This represents a partial sandbox escape, though the library's prototype protection mechanisms remain intact, limiting the overall impact.

Root Cause

The root cause lies in improper encapsulation of internal interpreter objects within the SandboxJS library. When the new operator is invoked within sandboxed code, the interpreter fails to properly isolate internal scope objects from the sandboxed execution context. This allows references to these internal objects to be captured and manipulated by untrusted code.

The vulnerability exists because the scope chain implementation does not adequately restrict which objects can be accessed through object instantiation operations. The internal interpreter scope objects become reachable through the new operator, breaking the intended isolation barrier.

Attack Vector

The attack vector for this vulnerability is network-based, as sandboxed code execution typically occurs in web applications or Node.js servers that process untrusted input. An attacker would craft malicious JavaScript code designed to exploit the scope leakage when executed within a SandboxJS sandbox.

The exploitation technique involves using the new operator in specific patterns to obtain references to internal interpreter objects. Once these references are obtained, the attacker can explore the scope hierarchy and potentially modify scope variables within the sandbox. While this does not enable full sandbox escape or prototype pollution, it does weaken the sandbox's security guarantees.

For detailed technical information on the exploitation mechanism, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-34217

Indicators of Compromise

• Unexpected modifications to sandbox scope variables during code execution
• Anomalous object creation patterns within sandboxed code that reference internal interpreter structures
• Error logs indicating access to objects outside the expected sandbox scope

Detection Strategies

• Monitor sandbox execution logs for unusual new operator usage patterns that may indicate exploitation attempts
• Implement runtime checks to detect when sandboxed code accesses unexpected scope objects
• Use dependency scanning tools to identify vulnerable versions of @nyariv/sandboxjs in your projects

Monitoring Recommendations

• Enable verbose logging for SandboxJS execution to track scope access patterns
• Implement application-level monitoring to detect behavioral anomalies in sandboxed code execution
• Set up alerts for dependency vulnerability notifications through npm audit or similar tools

How to Mitigate CVE-2026-34217

Immediate Actions Required

• Upgrade @nyariv/sandboxjs to version 0.8.36 or later immediately
• Review applications using SandboxJS to assess exposure to untrusted code execution
• Audit any code that was executed in vulnerable sandbox instances for potential compromise
• Consider implementing additional input validation for code submitted to the sandbox

Patch Information

The vulnerability is fixed in SandboxJS version 0.8.36. The patch addresses the scope leakage by properly isolating internal interpreter objects from sandboxed code. Organizations should update their npm dependencies using:

npm update @nyariv/sandboxjs

Verify the installed version with:

npm list @nyariv/sandboxjs

For more details on the fix, see the GitHub Security Advisory.

Workarounds

• If immediate upgrade is not possible, consider disabling or restricting sandbox functionality until patching is complete
• Implement additional application-level validation to restrict the use of the new operator in sandboxed code
• Use alternative sandboxing mechanisms as a temporary measure while planning the upgrade

# Verify current version and upgrade
npm list @nyariv/sandboxjs
npm install @nyariv/sandboxjs@0.8.36

# Audit for additional vulnerabilities
npm audit