Client.prototype.subsys = function(name, cb) {
  if (!this._sock
      || !this._sock.writable
      || !this._sshstream
      || !this._sshstream.writable)
    throw new Error('Not connected');

	return openChannel(this, 'session', function(err, chan) {
		if (err)
			return cb(err);

		reqSubsystem(chan, name, function(err, stream) {
			if (err)
				return cb(err);

			cb(undefined, stream);
		});
	});
};
The software constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.