CVE-2021-23449 (JavaScript, published 2021-10-18T17:15Z)
Description: value: This affects the package vm2 before 3.9.4 via a Prototype Pollution attack vector, which can lead to execution of arbitrary code on the host machine.
Severity: HIGH (CVSS v3 base score: 10)
Weakness: CWE-1321 \u2014 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.
Repository: https://github.com/patriksimek/vm2
Files changed:
lib/contextify.js
lib/main.js
lib/sandbox.js
test/vm.js
Commit message: Security Fixes


Vulnerable code:
function curry(func) {
const FunctionBind = curry(Function.prototype.bind);
const ObjectHasInstance = curry(local.Object[Symbol.hasInstance]);
/**
 * Creates the hook to check for the use of async.
 * 
 * @private
 * @param {*} internal - The internal vm object.
 * @return {*} The hook function
 */
function makeCheckAsync(internal) {
		if (hook === 'function' || hook === 'generator_function' || hook === 'eval' || hook === 'run') {
			const funcConstructor = internal.Function;
			if (args.findIndex(arg => /\basync\b/.test(arg)) === -1) return args;
			const asyncMapped = args.map(arg => arg.replace(/async/g, 'a\\u0073ync'));
				// Note: funcConstructor is a Sandbox object, however, asyncMapped are only strings.
				funcConstructor(...asyncMapped);
				// u is a sandbox object
				// Some random syntax error or error because of async.
				try {
					// Note: funcConstructor is a Sandbox object, however, args are only strings.
					funcConstructor(...args);
				} catch (e) {
					throw internal.Decontextify.value(e);
				// Then async error
				throw new VMError('Async not available');
		throw new VMError('Async not available');
		const hook = fixAsync ? makeCheckAsync(_internal) : null;
			script = this.options.strict ? code._compileNodeVMStrict() : code._compileNodeVM();
			script = new vm.Script(prefix +
					this._compiler(code, unresolvedFilename) + MODULE_SUFFIX, {
					script = new Script(code, {
		it('Dynamic import attack', (done) => {
			process.once('unhandledRejection', (reason) => {
				assert.strictEqual(reason.message, 'process is not defined');
				done();
			});
			vm2.run(`
				(async () => {
					try {
						await import('oops!');
					} catch (ex) {
						// ex is an instance of NodeError which is not proxied;
						const process = ex.constructor.constructor('return process')();
						const require = process.mainModule.require;
						const child_process = require('child_process');
						const output = child_process.execSync('id');
						process.stdout.write(output);
					}
				})();
			`);

Fixed code:
function uncurryThis(func) {
const FunctionBind = uncurryThis(Function.prototype.bind);
const ObjectHasInstance = uncurryThis(local.Object[Symbol.hasInstance]);
Contextify.connect(host.Function.prototype.bind, Function.prototype.bind);

const oldPrepareStackTraceDesc = Reflect.getOwnPropertyDescriptor(Error, 'prepareStackTrace');

let currentPrepareStackTrace = Error.prepareStackTrace;
const wrappedPrepareStackTrace = new host.WeakMap();
if (typeof currentPrepareStackTrace === 'function') {
	wrappedPrepareStackTrace.set(currentPrepareStackTrace, currentPrepareStackTrace);
}

let OriginalCallSite;
Error.prepareStackTrace = (e, sst) => {
	OriginalCallSite = sst[0].constructor;
};
new Error().stack;
if (typeof OriginalCallSite === 'function') {
	Error.prepareStackTrace = undefined;

	function makeCallSiteGetters(list) {
		const callSiteGetters = [];
		for (let i=0; i<list.length; i++) {
			const name = list[i];
			const func = OriginalCallSite.prototype[name];
			callSiteGetters[i] = {__proto__: null,
				name,
				propName: '_' + name,
				func: (thiz) => {
					return local.Reflect.apply(func, thiz, []);
				}
			};
		}
		return callSiteGetters;
	}

	function applyCallSiteGetters(callSite, getters) {
		const properties = {__proto__: null};
		for (let i=0; i<getters.length; i++) {
			const getter = getters[i];
			properties[getter.propName] = {
				__proto__: null,
				value: getter.func(callSite)
			};
		}
		return properties;
	}

	const callSiteGetters = makeCallSiteGetters([
		'getTypeName',
		'getFunctionName',
		'getMethodName',
		'getFileName',
		'getLineNumber',
		'getColumnNumber',
		'getEvalOrigin',
		'isToplevel',
		'isEval',
		'isNative',
		'isConstructor',
		'isAsync',
		'isPromiseAll',
		'getPromiseIndex'
	]);

	class CallSite {
		constructor(callSite) {
			Object.defineProperties(this, applyCallSiteGetters(callSite, callSiteGetters));
		}
		getThis() {return undefined;}
		getFunction() {return undefined;}
		toString() {return 'CallSite {}';}
	}

	(function setupCallSite() {
		for (let i=0; i<callSiteGetters.length; i++) {
			const name = callSiteGetters[i].name;
			const propertyName = callSiteGetters[i].propName;
			const func = {func() {
				return this[propertyName];
			}}.func;
			const nameProp = Object.getOwnPropertyDescriptor(func, 'name');
			nameProp.value = name;
			Object.defineProperty(func, 'name', nameProp);
			const funcProp = Object.getOwnPropertyDescriptor(OriginalCallSite.prototype, name);
			funcProp.value = func;
			Object.defineProperty(CallSite.prototype, name, funcProp);
		}
	})();

	Object.defineProperty(Error, 'prepareStackTrace', {
		configurable: false,
		enumerable: false,
		get() {
			return currentPrepareStackTrace;
		},
		set(value) {
			if (typeof(value) !== 'function') {
				currentPrepareStackTrace = value;
				return;
			}
			const wrapped = wrappedPrepareStackTrace.get(value);
			if (wrapped) {
				currentPrepareStackTrace = wrapped;
				return;
			}
			const newWrapped = (error, sst) => {
				if (host.Array.isArray(sst)) {
					for (let i=0; i<sst.length; i++) {
						const cs = sst[i];
						if (typeof cs === 'object' && local.Reflect.getPrototypeOf(cs) === OriginalCallSite.prototype) {
							sst[i] = new CallSite(cs);
						}
					}
				}
				return value(error, sst);
			};
			wrappedPrepareStackTrace.set(value, newWrapped);
			wrappedPrepareStackTrace.set(newWrapped, newWrapped);
			currentPrepareStackTrace = newWrapped;
		}
	});
} else if (oldPrepareStackTraceDesc) {
	Reflect.defineProperty(Error, 'prepareStackTrace', oldPrepareStackTraceDesc);
} else {
	Reflect.deleteProperty(Error, 'prepareStackTrace');
}
function tryCompile(args) {
	const code = args[args.length - 1];
	const params = args.slice(0, -1);
	vm.compileFunction(code, params);
}

function makeCheckHook(checkAsync, checkImport) {
	if (!checkAsync && !checkImport) return null;
		if (hook === 'function' || hook === 'generator_function' || hook === 'eval' || hook === 'run' ||
			(!checkAsync && (hook === 'async_function' || hook === 'async_generator_function'))) {
			const hasAsync = checkAsync && args.findIndex(arg => /\basync\b/.test(arg)) !== -1;
			const hasImport = checkImport && args.findIndex(arg => /\bimport\b/.test(arg)) !== -1;
			if (!hasAsync && !hasImport) return args;
			const mapped = args.map(arg => {
				if (hasAsync) arg = arg.replace(/async/g, 'a\\u0073ync');
				if (hasImport) arg = arg.replace(/import/g, 'i\\u006dport');
				return arg;
			});
				tryCompile(mapped);
				// Some random syntax error or error because of async or import.
				tryCompile(args);

				if (hasAsync && hasImport) {
					const mapped2 = args.map(arg => arg.replace(/async/g, 'a\\u0073ync'));
					try {
						tryCompile(mapped2);
					} catch (e) {
						throw new VMError('Async not available');
					}
					throw new VMError('Dynamic Import not supported');
				}
				if (hasAsync) {
					// Then async error
					throw new VMError('Async not available');
				throw new VMError('Dynamic Import not supported');
		if (checkAsync) throw new VMError('Async not available');
		return args;
		const hook = makeCheckHook(fixAsync, true);
			if (this._hook) {
				const prefix = this.options.strict ? STRICT_MODULE_PREFIX : MODULE_PREFIX;
				const scriptCode = prefix + code.getCompiledCode() + MODULE_SUFFIX;
				const changed = this._hook('run', [scriptCode])[0];
				if (changed === scriptCode) {
					script = this.options.strict ? code._compileNodeVMStrict() : code._compileNodeVM();
				} else {
					script = new vm.Script(changed, {
						filename: code.filename,
						displayErrors: false,
						importModuleDynamically
					});
				}
			} else {
				script = this.options.strict ? code._compileNodeVMStrict() : code._compileNodeVM();
			}
			let scriptCode = prefix + this._compiler(code, unresolvedFilename) + MODULE_SUFFIX;
			if (this._hook) {
				scriptCode = this._hook('run', [scriptCode])[0];
			}
			script = new vm.Script(scriptCode, {
					const ccode = vm._hook('run', [code]);

					script = new Script(ccode, {
		it('Dynamic import attack', () => {
			assert.throws(()=>vm2.run(`
				const process = import('oops!').constructor.constructor('return process')();
			`), /VMError: Dynamic Import not supported/);
	it('Error.prepareStackTrace attack', () => {
		const vm2 = new VM();
		const sst = vm2.run('Error.prepareStackTrace = (e,sst)=>sst;const sst = new Error().stack;Error.prepareStackTrace = undefined;sst');
		assert.strictEqual(vm2.run('sst=>Object.getPrototypeOf(sst)')(sst), vm2.run('Array.prototype'));
		assert.throws(()=>vm2.run('sst=>sst[0].getThis().constructor.constructor')(sst), /TypeError: Cannot read property 'constructor' of undefined/);
	});