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.
The SandboxJS library replaces the global `Function` constructor with a secure, controlled version (`SandboxFunction`), but before version 0.8.26 it did not include mapping of the `AsyncFunction`, `GeneratorFunction`, and `AsyncGeneratorFunction` constructors. These constructors are not global properties, but can be obtained via the `.constructor` property of an async function instance (e.g., `(async () => {}).constructor`). When code executed inside the sandbox accesses `.constructor` on an async function, the `executor.ts` module returns the native, unmodified host `AsyncFunction` constructor, as it is not on the list of safe replacements. Using this constructor, an attacker can create functions executed outside the sandbox context, completely bypassing its restrictions.
An attacker can execute arbitrary JavaScript code outside the sandbox in the full context of the host environment (RCE), gaining access to all resources and data available to the application — including the file system, environment variables, and network.
SandboxJS should be updated to version 0.8.26 or later, which introduces proper mapping of `AsyncFunction`, `GeneratorFunction`, and `AsyncGeneratorFunction` constructors in the sandbox isolation mechanism.
Nyariv SandboxJS library in versions prior to 0.8.26
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:HNyariv Sandboxjs
APPNyariv< 0.8.26
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