CVE-2026-92956: vm2 sandbox escape via WebAssembly.compileStreaming Promise species bypass

There is a sandbox escape in vm2 3.11.5 / current HEAD when it is used on Node.js 26. The issue is reachable from a default new VM() sandbox. No NodeVM, require permission, host object injection, or intentionally unsafe configuration is required.

The escape is a patch-bypass of the same security invariant addressed by GHSA-6j2x-vhqr-qr7q. The earlier fix removed the JSPI entry points WebAssembly.promising and WebAssembly.Suspending, because those APIs exposed a Promise path whose host-realm Promise.prototype was not intercepted by vm2’s Promise hardening or bridge layer.

The same unsafe class remains reachable through WebAssembly.compileStreaming and WebAssembly.instantiateStreaming. On Node 26, these streaming APIs can produce a raw host-realm Promise path that rejects with a host-realm error. By controlling Symbol.species through Promise.prototype.finally, sandbox code can receive that raw host error object, walk from the host error constructor to the host Function constructor, and recover the real host process object.

The proof of concept demonstrates this by first showing that direct access to process, require, and constructor-based escapes are blocked in the same default VM. It then reaches the host process, verifies that the recovered pid matches the parent Node process, and writes a harmless marker file through host fs.