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

Title:SandboxJS has Sandbox Escape via Unprotected AsyncFunction Constructor (CVE-2026-23830)
Description: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.

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