CVE-2026-23830
CRITICALSandboxJS has Sandbox Escape via Unprotected AsyncFunction Constructor
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@nyariv/sandboxjsnpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @nyariv/sandboxjs | all versions | 0.8.26 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @nyariv/sandboxjs. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @nyariv/sandboxjs to 0.8.26 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23830 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.
How O3 protects you
O3 pinpoints whether CVE-2026-23830 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-23830. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-23830 in your dependencies?
O3 detects CVE-2026-23830 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.