CVE-2026-23830 SandboxJS has Sandbox Escape via Unprotected AsyncFunction Constructor
Attackers can escape the SandboxJS sandbox by accessing the unprotected AsyncFunction constructor, leading to remote code execution on the host.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23830?
CVE-2026-23830 is a critical code injection vulnerability in nyariv SandboxJS, published on 27 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-23830?
2 open source packages ship an affected version, including @nyariv/sandboxjs. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
@nyariv/sandboxjs npm | All versions | 0.8.26 |
@nyariv/sandboxjs npm | All versions | 0.8.26 |
Products include Nyariv Sandboxjs.
How do I fix CVE-2026-23830?
Upgrade @nyariv/sandboxjs to 0.8.26 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-23830 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-23830 exists.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in nyariv SandboxJS
- CVE-2026-43898 SandboxJS: Sandbox escape via Function.caller leakage of internal call op
- CVE-2026-34208 SandboxJS: Sandbox integrity escape
- CVE-2026-26954 SandboxJS has a Sandbox Escape
- CVE-2026-25520 SandboxJS has a Sandbox Escape
- CVE-2026-25586 SandboxJS has a Sandbox Escape via Prototype Whitelist Bypass and Host Prototype Pollution
Sources
Also known as GHSA-wxhw-j4hc-fmq6.