SandboxJS Sandbox Escape via Unprotected AsyncFunction Constructor (CVE-2026-23830)
CVE-2026-23830 is a maximum-severity (CVSS 10.0) sandbox-escape vulnerability in SandboxJS, a library intended to safely execute untrusted JavaScript. The issue allows attackers to break out of the sandbox and achieve arbitrary code execution on the host by leveraging gaps in SandboxJS’s “safe replacement” model for dangerous constructors.
The flaw stems from SandboxJS mapping the global Function constructor to a sandboxed equivalent, but (in affected versions) failing to similarly isolate the “Async” and generator constructor families: AsyncFunction, GeneratorFunction, and AsyncGeneratorFunction. Although these constructors are not directly exposed as globals, they can be obtained via an instance’s .constructor (e.g., (async () => {}).constructor); because the executor returns the native host AsyncFunction when it is not present in the safe-replacement map, an attacker can create new functions that execute in the global scope and bypass sandbox restrictions. SandboxJS 0.8.26 is reported as the patched version.
Timeline
Jan 28, 2026
CVE-2026-23830 disclosure details SandboxJS sandbox escape
Public disclosure described CVE-2026-23830 as a maximum-severity flaw in SandboxJS caused by missing protections for asynchronous and generator function constructors. Attackers could access the native host AsyncFunction via the .constructor property and escape the sandbox to gain full host access.
Jan 28, 2026
SandboxJS releases version 0.8.26 to fix CVE-2026-23830
SandboxJS fixed a critical sandbox escape vulnerability in version 0.8.26 by properly isolating AsyncFunction, GeneratorFunction, and AsyncGeneratorFunction within its sandboxing mechanism. The flaw affected all versions prior to 0.8.26 and could allow arbitrary code execution outside the sandbox.
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