10

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-23830

CVE-2026-23830: SandboxJS has Sandbox Escape via Unprotected AsyncFunction Constructor

SandboxJS is a JavaScript sandboxing library. Versions prior to 0.8.26 have a sandbox escape vulnerability due to AsyncFunction not being isolated in SandboxFunction. The library attempts to sandbox code execution by replacing the global Function constructor with a safe, sandboxed version (SandboxFunction). This is handled in utils.ts by mapping Function to sandboxFunction within a map used for lookups. However, before version 0.8.26, the library did not include mappings for AsyncFunction, GeneratorFunction, and AsyncGeneratorFunction. These constructors are not global properties but can be accessed via the .constructor property of an instance (e.g., (async () => {}).constructor). In executor.ts, property access is handled. When code running inside the sandbox accesses .constructor on an async function (which the sandbox allows creating), the executor retrieves the property value. Since AsyncFunction was not in the safe-replacement map, the executor returns the actual native host AsyncFunction constructor. Constructors for functions in JavaScript (like Function, AsyncFunction) create functions that execute in the global scope. By obtaining the host AsyncFunction constructor, an attacker can create a new async function that executes entirely outside the sandbox context, bypassing all restrictions and gaining full access to the host environment (Remote Code Execution). Version 0.8.26 patches this vulnerability.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-23830

CVE-2026-23830:

10

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
@nyariv/sandboxjs	npm	< 0.8.26	0.8.26

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability is a sandbox escape in SandboxJS caused by the failure to sandbox the AsyncFunction constructor. The root cause lies in the createExecContext function in src/utils.ts. This function is responsible for setting up the sandboxed environment, including a map of native functions to their safe, sandboxed replacements.

The analysis of the patch 345aee6566e47979dee5c337b925b141e7f78ccd reveals that createExecContext was modified to add a mapping for AsyncFunction. Before this patch, the function only sandboxed the Function constructor, but not AsyncFunction, GeneratorFunction, or AsyncGeneratorFunction.

When code inside the sandbox accessed the .constructor property of an async function (e.g., (async () => {}).constructor), the executor would not find a sandboxed replacement in the map created by createExecContext. Consequently, it would return the original, powerful AsyncFunction constructor from the host environment. An attacker could then use this constructor to create and execute a new function outside of the sandbox's restrictions, achieving remote code execution.

Therefore, createExecContext is identified as the vulnerable function because its incomplete setup of the sandbox environment is the direct cause of the vulnerability.

Vulnerable functions

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WAF Rule

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Reasoning

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