امنیت سوئیچ LAN: آنچه هکرها در مورد سوئیچ های شما می دانند

I have been promoting the need to protect access to local network infrastructures (against the insider threat) for so many years that I’m even tired of sending the same message again and again these days, but I do not give up. I never understood why if we require authentication to each and every technology resource, such as your computer operating system, servers, databases, applications, and even physical facilities, why this has not been the case to access the network. Still today, lots of local networks from big companies and organizations are “free”, that is, if the attacker gets physical access to an Ethernet port (RJ-45 connector) he is in! (the network). This is one of the attacker’s dreams, and we can simply mitigate this threat through the 802.1X protocol. The expansion of wireless networks has helped a lot to promote it, but still it must be applied to most wired networks out there.

802.1X is just one of the multiple additions you can make to your layer 2 security stance in order to protect the local (layer 2) network infrastructure from several attacks. Definitely, you need to stop thinking about IP (layer 3) attacks only, and move one level down. Honestly, one of the layer 2 attacks that works 99% of the times I’m running an internal penetration test is ARP spoofing or poisoning. I tried to emphasize the impact of this attack and the associated defenses on my first GIAC paper for the Incident Handler (GCIH) certification in 2003, “Real World ARP Spoofing”.

The book covers most of the vulnerabilities, design flaws, and security holes associated to the layer 2 protocols we currently and extensively use on our networks, such as MAC flooding and spoofing attacks, and STP, VLAN, DHCP, ARP, PoE, HSRP, VRRP, CDP, VTP, LAP and even layer-2 IPv6 related attacks. However, and starting with the minimum privilege principle (if you don’t need it, why it is enabled?), the main focus of this book (and specially Part I) is to provide the reader with the knowledge and specific details to detect these attacks and protect the network and network devices (mainly switches) against all these threats. For each protocol and attack it describes the proper settings for a secure implementation.

Parts II of the book focuses on Denial of Service (DoS and DDoS) attacks on layer 2 devices and provide an excellent overview of switches architectures, internal implementation details (mainly Cisco focused), the relationships between the Control Plane and the Data Plane, the protocols each layer deals with, and the security implications on the internal operation of switches. If you want to know how your switches really work and the security implications of enabling/disabling certain capabilities, this is the section of the book you must read.

Part III then provides an introduction to more advanced access control options, through multiple ACL types, and layer-2 authentication (802.1X). It’s a good introduction to go deeper into serious layer-2 access control and authentication projects and deployments.

Simplifying the threat, the attackers have a single tool (in fact they have multiple but this is THE tool) to do real damage at layer 2, Yersinia, co-develop by a Spanish security colleague, David. We, as defenders, need to properly design and deploy all the layer 2 technologies and protocols considering the security implications of its presence on the network. Fortunately enough, the countermeasures available to mitigate layer 2 risks are available in some current network devices, mainly switches. BTW, I encourage you to use the attack tools, like Yersinia, to audit your network. Some of the book countermeasures are trivial to apply, while some others require a very carefully thought-out planning. The book provides the guidance you need to start accomplishing the goal of getting a definitive layer 2 protected network by exposing the complexity, advantages and disadvantages of each solution.

The book is structured in small, easy to read, chapters that describe each of the technologies analyzed and its operation, the security issues and attack examples, and the detection and protection mechanisms you need to apply, straight to the most relevant implementation details. It also includes practical examples and describes multiple scenarios where each countermeasure can be applied, as well as the main decision factors to apply it in a given way. If you are busy (and who is not these days?), I recommend you to select a layer 2 protocol or technology you are using, select the appropriate chapter (a 30-45 minutes read at most), and start planning and applying the related security best practices. You can repeat this chapter selection process every couple of weeks, and in 2-3 months your network will be what I would like to see on all my customers. The book allows network administrators and infosec professionals to independently digest any of the chapters and start protecting the associated technology. Obviously, the main goal should be to apply all the book recommendations to your infrastructure in the short-mid term. Unfortunately, not all the countermeasures mentioned are available in all switches; there is still lot of work to be done by the vendors to implement all them.

The book opens the doors to a whole set of layer-2 threats, but it is not a complete guide to implement all the related protections, neither a command documentation book. It is up to the reader to check his switch documentation (Cisco or others) to get the full syntax details and multiple options for each of the countermeasures detailed. If you have managed Cisco devices, you know syntax also changes between IOS/CatOS versions, so I prefer this approach rather than a detailed syntax compendium that may be unusable on my specific IOS/CatOS version.

Even this is a Cisco Press book, and obviously it is focused on the current solutions available from Cisco, it is fair to admit that Cisco is leading the networking market and includes some of the most advanced layer 2 protection mechanisms in its switches, such as port security, UUFP, root and BPDU guard, BPDU filtering and rate-limiting, VLAN and layer-2 protocols best practices, DHCP snooping, DHCP rate-limiting and validation, IP source guard, DAI (Dynamic ARP Inspection), PoE defenses, HSRP and VRRP strong authentication, 802.1X, and lots of ACLs types: . RACL, VACL, PACLs, etc. Therefore, as this is the way to go, other vendors (if they do not already have these) should provide similar protection capabilities on their layer 2 network devices.

I specially liked how the book ends up (Part IV) covering LinkSec, 802.1AE and 802.1af, future standards that will finally provide confidentiality and integrity at layer 2 at wire-speeds, similarly to what be have today in wireless networks with 802.11i (WPA and WPA2). Why don’t you start checking if these standards are supported by your endpoint (client, servers, printers, VoIP phones, etc) and network devices? The sooner we use it, the better.

The only portion missing on the book IMHO is the inclusion of layer 2 QoS protocols, such as 802.1p. Apart from that, chapter 1 is a light intro to security. If you have been in the field for a while, you can directly jump over it. I think it could have been omitted.

Before reading this book, I had an extensive previous experience on layer 2 security, switches, layer 2 penetration testing, and layer 2 network security architectures and design, and I really enjoyed the book, specially its practical focus, broad scope on layer 2 issues, the format and examples. If you are a penetration tester, I’m sure you will get a few ideas too for your next challenge, and you can easily apply them as most attack tools are publicly available and included on the latest Backtrack 3 version. Definitely, if you are a network security professional or network administrator in any way, shape or form, this book must be in your shelves.

Full-review: http://radajo.blogspot.com/2008/07/security-book-review-lan-switch.html