SMB – 1 billion vulnerable machines

An Introduction to SMB for Network Security Analysts by Nate “Doomsday” Marx.

Of all the common protocols a new analyst encounters, perhaps none is quite as impenetrable as Server Message Block (SMB). Its enormous size, sparse documentation, and wide variety of uses can make it one of the most intimidating protocols for junior analysts to learn. But SMB is vitally important: lateral movement in Windows Active Directory environments can be the difference between a minor and a catastrophic breach, and almost all publicly available techniques for this movement involve SMB in some way. While there are numerous guides to certain aspects of SMB available, I found a dearth of material that was accessible, thorough, and targeted towards network analysis. The goal of this guide is to explain this confusing protocol in a way that helps new analysts immediately start threat hunting with it in their networks, ignoring the irrelevant minutiae that seem to form the core of most SMB primers and focusing instead on the kinds of threats an analyst is most likely to see. This guide necessarily sacrifices completeness for accessibility: further in-depth reading is provided in footnotes. There are numerous simplifications throughout to make the basic operation of the protocol more clear; the fact that they are simplifications will not always be highlighted. Lastly, since this guide is an attempt to explain the SMB protocol from a network perspective, the discussion of host based information (windows logs, for example) has been omitted.

It never occurred to me that NTLM, introduced with Windows NT in 1993, is still supported in the latest version of Windows.

That means a deep knowledge of SMB pushes systems vulnerable to you almost north of 1 billion.

How’s that for a line in your CV?

Comments are closed.