Bypass MAC filtering – the physical assessor



In this article we are going to discuss about how to bypass MAC filtering. An attacker needs to be aware of methods for remote compromise: attacking the VPN, wireless infiltration from a distance using high-gain antennas, and so forth. However, the pen tester can never forget the big picture. This is a field where it’s very easy to get caught up in the highly specific technical details and miss the human element of security design.

There’s a design flaw concept that pen testers like to call the candy bar model. This simply refers to a network that is tough and crunchy on the outside, but gooey on the inside. In other words, it’s a model that emphasizes the threats of the outside world when designing the security architecture, while assuming that someone who is physically inside company facilities has been vetted and is therefore trusted. The mindset here dates back many years; in the earliest days of what became the internet, the physical access points to the network were inside highly secure facilities. Packets coming in over the network were safely assumed to be from a secure environment and sent by an authorized individual. In today’s world, a packet hitting the border of a company’s network could be from an authorized individual on a business trip, or it could be from a clever teenager in Thailand eager to try out some newly learned tricks.

The candy bar model will come up in later chapters when we discuss other network attacks. Once you crack that outer shell, you’ll often find that the path forward seems paved especially for you—and a successful compromise will inform your client of the devastating consequences of this mistaken assumption.

How you social engineer your target is a subject for another book altogether, but for the purposes of this discussion, let’s assume that you have physical access to network drops. Not all physical access is the same, though: if you convinced your target to hire you as a full-time employee, then you’ll have constant physical access. They’ll even hand you a computer. However, what’s more likely is that you’ve exploited a small gap in their physical security stance, and your presence can be undetected or tolerated for only a short period of time. You’ve snuck in through the smoker’s door

after striking up some conversation with an unwitting employee; you’ve been given permission to walk around for an hour with a convincing-looking contractor uniform and clipboard; or (my personal favorite) you’ve earned trust and affection by bringing in a big box of doughnuts for the people expecting an auditor’s visit based on a well-scripted phone call. We’ll demonstrate how to set up a Kali box to function as a rogue wireless access point while impersonating the MAC address of a VoIP phone.



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