For this chapter, we'll be using a Windows XP image named cridex.vmem, which can be downloaded directly from https://github.com/volatilityfoundation/volatility/wiki/Memory-Samples.
Select the link with the Description column, Malware - Cridex to download the cridex.vmem image:
There are many other images on this page that are also publicly available for analysis. To practice working with the Volatility Framework and further enhance your analytical skills, you may wish to download as many as you like and use the various plugins available in Volatility.