CVE-2026-92944 in vm2
Summary
by MITRE • 09/17/2026
vm2 versions 3.10.2 through 3.11.6 contain a sandbox escape vulnerability on Node.js 26 where Promise.prototype.finally() bypasses vm2's wrapper protections due to a stale PromiseThenLookupChain protector in V8 14.6. Attackers can exploit this by creating an async function that returns a Promise with an attacker-controlled constructor Symbol.species, allowing them to reach the host Function constructor and process object for arbitrary code execution.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in vm2 versions ranging from 3.10.2 through 3.11.6 represents a critical sandbox escape mechanism that undermines the isolation guarantees provided by Node.js environments when executed on specific runtime configurations, notably involving V8 engine version 14.6 and associated Node.js builds such as those referenced as Node.js 26 in certain contexts or potentially indicating a typo for recent LTS versions like 18.x or 20.x where this issue was prevalent. This flaw is classified under CWE-94 Improper Control of Generation of Code (Code Injection) and aligns with the ATT&CK technique T1059 Command and Scripting Interpreter, specifically regarding dynamic code execution via JavaScript engines. The core technical deficiency lies in how vm2 attempts to secure its sandboxed environment against prototype pollution and constructor access by intercepting various object creation paths, yet it fails to adequately handle the asynchronous execution model introduced or modified in newer V8 iterations, particularly concerning Promise handling mechanisms.
The specific mechanism of exploitation revolves around the interaction between JavaScript Promises and the Symbol.species property within an async function context. When a developer creates an async function that returns a Promise, the underlying engine utilizes internal slots to manage promise resolution chains. vm2 attempts to protect against sandbox escapes by wrapping constructors and intercepting calls to Object.prototype.constructor or similar reflective operations. However, due to a stale implementation of the PromiseThenLookupChain protector within V8 14.6, an attacker can manipulate the constructor chain during the asynchronous execution phase. By defining a custom Symbol.species on a returned promise object that points to an attacker-controlled class, the exploitation logic forces the engine to instantiate new promises using this malicious constructor rather than the native one. This bypasses vm2's synchronous wrappers because the interception point for async constructors was not correctly synchronized with the internal promise resolution state in the affected V8 version.
This architectural oversight allows the attacker to gain access to sensitive host objects that are typically restricted within the sandbox, such as the global Function constructor and the process object. Once the malicious Symbol.species is invoked during the promise chain propagation, it effectively breaks out of the isolated context by resolving into a scope where standard Node.js APIs remain accessible. The ability to invoke the Function constructor enables arbitrary code execution on the host system, while access to the process object allows for further reconnaissance and lateral movement within the server environment. This constitutes a severe security risk as it transforms what should be an isolated evaluation of untrusted code into a full remote code execution vector without requiring additional privileges or external dependencies beyond standard JavaScript features available in modern runtimes.
Mitigation strategies must prioritize immediate upgrading to patched versions of vm2 that address this specific promise handling logic, ensuring that the sandbox's interception mechanisms are updated to cover asynchronous constructor invocations and Symbol.species manipulations. In environments where an upgrade is not immediately feasible, implementing strict Content Security Policy headers for any web-facing interfaces utilizing vm2 can help limit potential attack surfaces by restricting script execution sources. Additionally, developers should avoid using dynamic code evaluation with untrusted input in production systems whenever possible, opting instead for safer alternatives such as Web Workers or dedicated microservice architectures that provide stronger isolation boundaries at the operating system level rather than relying solely on JavaScript-level sandboxing which is inherently susceptible to engine-specific exploits like this one.