Is it illegal to practice with vulnhub machines?

In the field of ethical hacking, the distinction between legal skill-building and criminal activity is defined primarily by authorization and consent. Legislation such as the Computer Misuse Act (CMA) 1990 makes it a criminal offense to access computer material without explicit permission from the owner. However, practicing with "VulnHub" machines is entirely legal and considered an industry best practice for developing technical proficiency.

VulnHub provides intentionally vulnerable virtual machine (VM) images that researchers download and run within their own isolated, local environments. Because the individual practicing is the owner and administrator of the physical host machine and the virtualized target, they have absolute "authorization" to conduct testing. These machines are specifically designed to be disconnected from external networks or organizations, ensuring that the hacking activity remains confined to a "safe lab" environment.

Practicing in such a sandbox allows an ethical hacker to refine their exploitation techniques—such as reconnaissance, scanning, and gaining access—without risk of harming third-party systems or violating privacy laws. It provides a controlled setting where the "intent" is educational rather than malicious. Conversely, testing these same techniques against any external website or network without a formal contract and written scope would be a serious crime punishable by imprisonment. Therefore, using locally hosted vulnerable labs like VulnHub is not only legal but essential for any professional aspiring to earn certifications like the OSCP while staying within the confines of ethical and legal boundaries.