CVE-2026-92942 in vm2
Summary
by MITRE • 09/17/2026
vm2 before 3.11.7 (affected versions <= 3.11.6) does not enforce the VM({ timeout }) option on code executed outside the synchronous VM#run() call. The timeout only wraps the single call to _runScript() via doWithTimeout() in lib/vm.js, and FinalizationRegistry and WeakRef are exposed to sandboxed code unmodified (they are not among the hardened globals in lib/setup-sandbox.js). Sandboxed code can register a FinalizationRegistry cleanup callback against an object and then drop the only strong reference to it; vm.run() returns within the configured timeout, but when the V8 garbage collector later reclaims the object it invokes the sandboxed cleanup callback outside any vm2 timeout accounting. A busy loop in that callback blocks the host event loop for an unbounded period, resulting in denial of service. The time of invocation depends on the garbage collector (e.g. under memory pressure or with --expose-gc).
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in versions of vm2 prior to 3.11.7 represents a critical failure in resource management and sandbox isolation, specifically concerning how asynchronous cleanup operations interact with execution timeouts. The core technical flaw lies in the incomplete enforcement of the timeout parameter when code is executed outside the synchronous VM#run() call. While the library attempts to wrap single script executions via doWithTimeout(), this mechanism fails to account for lifecycle events that occur after the primary execution context has returned. Specifically, FinalizationRegistry and WeakRef are exposed to sandboxed code without modification or restriction. These JavaScript features allow developers to register cleanup callbacks that execute when specific objects are garbage collected. Because these globals are not included in the hardened global list within lib/setup-sandbox.js, malicious actors can exploit them to bypass intended execution limits.
The operational impact of this flaw is a severe denial of service condition for the host application. An attacker can craft sandboxed code that registers a FinalizationRegistry cleanup callback against an object and then immediately drops all strong references to that object. The vm.run() method will complete its execution within the configured timeout, creating a false sense of security regarding resource containment. However, when the V8 garbage collector eventually reclaims the unreferenced object, it invokes the registered sandboxed cleanup callback outside any active vm2 timeout accounting mechanisms. If this callback contains even a simple busy loop or computationally intensive task, it will block the host event loop for an unbounded period. This effectively freezes the Node.js process, rendering the application unresponsive to new requests and causing significant service disruption.
The timing of this exploitation is non-deterministic as it depends on the internal behavior of the V8 garbage collector. The cleanup callback may not execute immediately but rather when memory pressure increases or if specific flags like --expose-gc are utilized during runtime testing. This unpredictability makes the vulnerability particularly dangerous in production environments where resource constraints vary dynamically. From a classification perspective, this issue aligns with CWE-400, which describes uncontrolled resource consumption leading to denial of service conditions. Furthermore, it relates to CWE-697 regarding incorrect comparison operations if one considers the failure to properly bound execution time across all code paths as an error in logical control flow enforcement.
To mitigate this vulnerability, organizations must immediately upgrade vm2 to version 3.11.7 or later where these sandboxing gaps have been addressed. In environments where upgrading is not immediately feasible, it is crucial to avoid exposing FinalizationRegistry and WeakRef to untrusted code within the VM context. Implementing strict allowlists for global objects during sandbox initialization can prevent access to these dangerous APIs. Additionally, deploying runtime monitoring tools that detect prolonged blocking of the event loop can help identify such attacks early. Security teams should also review any custom implementations of garbage collection callbacks in their applications to ensure they do not perform heavy operations without proper throttling or timeout mechanisms independent of the VM sandbox constraints.