UNIX and Linux Security
UNIX, Linux, and other similar operating systems are gaining in popularity and market share. UNIX is still a dominant player in the server arena.
UNIX, Linux, FreeBsd, AIX, and so on (all referred to as UNIX in this tutorial) have great potential for both being very secure and being exploited. Some of the same features that make UNIX a good target for security attacks make it powerful enough to be operated safely.
UNIX as a target
There is an ongoing debate among system administrators as to whether Windows or UNIX is the more vulnerable operating system. This debate often degrades to a mere count of vulnerabilities applicable to one side or the other. In any case, it is useful to start with an examinaton of why UNIX and Linux might be a target of security attacks. The following lists the four main reasons that UNIX is a target:
- Linux (and much of the other UNIX implementations) are open source.
- UNIX installations are easy to obtain, both in terms of being inexpensive (often free) and readily distributed.
- Most hacking tools are available for UNIX.
- UNIX is a good environment to exchange hacks and code.
Open source means products made available along with the source code needed to rebuild or recompile the products. Open source does not mean free of cost or licenses, although it is in many cases.
Many people view open source as a major security threat. In fact, this has not turned out to be the case. While it is true that a hacker can get a head start on finding security issues by examining the code, this concern is certainly overrated, because of the extremely long hours that would be required to walk through the thousands of lines of code. However, once a flaw is identified, the source code can be very useful to the hacker in developing an exploit.
Ironicly, over time, the ultimate effect of having code open to all may be that the code is better and more secure. Problems tend to be quickly fixed and thoroughly vetted. This is discussed in more detail in the section "Open Source Issues" later in this tutorial.
Easy-to-obtain operating system
That Linux is low cost and freely distributed on the Internet makes it a popular operating system for experimentation. Many public forums exist in which novices can get help and support for their Linux implementation. Even solutions for complicated and obscure problems can be found with a minimal amount of searching on the Internet. If it is a popular operating system to use, it can be expected to be popular for hacking as well.
In this tutorial:
- Network and development tools
- UNIX/Linux as a poor target
- Open source issues
- Detecting hardware changes
- Disk partitioning
- Prepare for the eventual attack
- Controlling the Configuration
- Kernel configurations
- Kernel modules
- proc file system
- Operating UNIX Safely
- Uncommon services
- Processes controlling processes
- The chkconfig command
- Controlling users
- Encryption and certificates
- Hardening UNIX
- Packet filtering with iptables