vm2 through 3.12.0 (fixed in 3.12.1) does not correctly handle a nullish "this" receiver in the apply trap of its bridge (lib/bridge.js): when sandboxed code calls a host-provided non-strict (sloppy-mode) function without a receiver — e.g. "fn()", a detached method, "fn.call()", "fn.apply(undefined)", "Reflect.apply(fn, undefined, [])", or "fn.bind()()" — the undefined receiver is passed straight through to the host call, and V8 substitutes the host realm's global object for "this". vm2 then wraps and returns that object to the sandbox, giving sandboxed script a live proxy of the host global. This allows a complete sandbox escape: untrusted script can reach "process" and execute arbitrary code/commands on the host (for example via "process.getBuiltinModule('child_process').execSync"). Exploitation requires that the embedding application expose at least one non-strict host function to the sandbox; strict-mode and ES module host functions are not affected.