The dns-sync library for node.js allows resolving hostnames in a synchronous fashion. All versions of dns-sync prior to the release 0.1.3 were vulnerable to arbitrary command execution via maliciously formed hostnames.
var dnsSync = require('dns-sync'); console.log(dnsSync.resolve('$(id > /tmp/foo)'));
This is caused by the hostname being passed through a shell as part of a command execution.
Upgrade dns-sync to version 0.1.1 or greater.