Linux Firewalls: Attack Detection and Response with iptables, psad, and fwsnort

Linux Firewalls: Attack Detection and Response with iptables, psad, and fwsnort

Michael Rash

Language: English

Pages: 336

ISBN: 1593271417

Format: PDF / Kindle (mobi) / ePub


System administrators need to stay ahead of new security vulnerabilities that leave their networks exposed every day. A firewall and an intrusion detection systems (IDS) are two important weapons in that fight, enabling you to proactively deny access and monitor network traffic for signs of an attack.

Linux Firewalls discusses the technical details of the iptables firewall and the Netfilter framework that are built into the Linux kernel, and it explains how they provide strong filtering, Network Address Translation (NAT), state tracking, and application layer inspection capabilities that rival many commercial tools. You'll learn how to deploy iptables as an IDS with psad and fwsnort and how to build a strong, passive authentication layer around iptables with fwknop.

Concrete examples illustrate concepts such as firewall log analysis and policies, passive network authentication and authorization, exploit packet traces, Snort ruleset emulation, and more with coverage of these topics:

  • Passive network authentication and OS fingerprinting
  • iptables log analysis and policies
  • Application layer attack detection with the iptables string match extension
  • Building an iptables ruleset that emulates a Snort ruleset
  • Port knocking vs. Single Packet Authorization (SPA)
  • Tools for visualizing iptables logs

    Perl and C code snippets offer practical examples that will help you to maximize your deployment of Linux firewalls. If you're responsible for keeping a network secure, you'll find Linux Firewalls invaluable in your attempt to understand attacks and use iptables-along with psad and fwsnort-to detect and even prevent compromises.

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    Layer Attacks and Defense This chapter shows the types of attacks that exist in the network layer and what you can do about them. I’ll introduce you to the iptables logging format and emphasize the network layer information that you can glean from iptables logs. Chapter 3: Transport Layer Attacks and Defense The transport layer is the realm of server reconnaissance with port scans and sweeps, and this chapter examines the inner workings of these methods. The iptables logging format is well suited

    Defense ............................................................69 Chapter 5: Introducing psad: The Port Scan Attack Detector ...............................................81 Chapter 6: psad Operations: Detecting Suspicious Traffic ..................................................99 Chapter 7: Advanced psad Topics: From Signature Matching to OS Fingerprinting .............113 Chapter 8: Active Response with psad...........................................................................131

    a kernel crash, as discussed in more detail at http://isec.pl/vulnerabilities/isec-0018-igmp.txt. Kernel code sometimes contains security bugs, and these bugs can exist all the way down at the network layer processing code or within device drivers. 44 C ha pt er 2 Network Layer Responses Agreeing on definitions for network layer responses is as useful as agreeing on definitions for network layer attacks. Because such responses should not involve information that resides at the transport layer

    received on a port. If the port is closed, then TCP responds with a RST/ACK, but if the port is open, TCP does not respond with any packet at all. The following example shows a FIN scan of the iptablesfw system, and note at that all ports are reported as open|filtered by Nmap. Because a surprise FIN packet is not part of any legitimate TCP connection, all of the FIN packets (even those to open ports) are matched against the INVALID state rule in the iptables policy and subsequently logged and

    host level stack-hardening mechanisms (see the PaX project at http://pax.grsecurity.net) to inline network devices with software that can prevent malicious packets from ever reaching their intended targets, while simultaneously allowing all other traffic through unimpeded. In contrast, active response refers to the set of mechanisms that can be employed against an attacker (once an attack is detected) that do not necessarily thwart the attack. The fact that active response isn’t always able to

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