Securing Debian is not very different from securing any other system; in order to do it properly, you must first decide what you intend to do with it. After this, you will have to consider that the following tasks need to be taken care of if you want a really secure system.
You will find that this manual is written from the bottom up, that is, you will read some information on tasks to do before, during and after you install your Debian system. The tasks can also be thought of as:
The following manual does not (usually) go into the details on why some issues are considered security risks. However, you might want to have a better background regarding general UNIX and (specific) Linux security. Take some time to read over security related documents in order to make informed decisions when you are encountered with different choices. Debian GNU/Linux is based on the Linux kernel, so much of the information regarding Linux, as well as from other distributions and general UNIX security also apply to it (even if the tools used, or the programs available, differ).
Some useful documents include:
Linux Security HOWTO(also available at
LinuxSecurity) is one of the best references regarding general Linux Security.
Security Quick-Start HOWTO for Linuxis also a very good starting point for novice users (both to Linux and security).
Linux Security Administrator's Guide(provided in Debian through the
lasgpackage) is a complete guide that touches all the issues related to security in Linux, from kernel security to VPNs. Note that it has not been updated since 2001, but some information is still relevant. 
Securing Linux Step by Step.
Securing and Optimizing Linux: RedHat Editionyou can find a similar document to this manual but related to RedHat, some of the issues are not distribution-specific and also apply to Debian.
Securing your Domain HOWTO.
Secure Programs HOWTO(master copy is available at
http://www.dwheeler.com/secure-programs/, it includes slides and talks from the author, David Wheeler)
Firewall HOWTOand the
IPCHAINS HOWTO(for kernels previous to 2.4).
Linux Security ReferenceCard
In any case, there is more information regarding the services explained here
(NFS, NIS, SMB...) in many of the HOWTOs of the
The Linux Documentation Project. Some
of these documents speak on the security side of a given service, so be sure to
take a look there too.
The HOWTO documents from the Linux Documentation Project are available in
Debian GNU/Linux through the installation of the
(text version) or
doc-linux-html (html version). After
installation these documents will be available at the
/usr/share/doc/HOWTO/en-html directories, respectively.
Other recommended Linux books:
Hacking Linux ExposedBy Brian Hatch. McGraw-Hill Higher Education. ISBN 0072127732. April, 2001
Other books (which might be related to general issues regarding UNIX and security and not Linux specific):
Practical Unix and Internet Security (2nd Edition)Garfinkel, Simpson, and Spafford, Gene; O'Reilly Associates; ISBN 0-56592-148-8; 1004pp; 1996.
Some useful Web sites to keep up to date regarding security:
Security Focusthe server that hosts the Bugtraq vulnerability database and list, and provides general security information, news and reports.
Linux Security. General information regarding Linux security (tools, news...). Most useful is the
Linux firewall and security site. General information regarding Linux firewalls and tools to control and administrate them.
Just so you have a general overview of security in Debian GNU/Linux you should take note of the different issues that Debian tackles in order to provide an overall secure system:
Debian Social Contractstates:
We Won't Hide Problems
We will keep our entire bug-report database open for public view at all times. Reports that users file on-line will immediately become visible to others.
Bugtraq, on the lookout for packages with security issues that might be included in Debian.
This document as well, tries to enforce a better distribution security-wise, by publishing security information specific to Debian which complements other information-security documents related to the tools used by Debian or the operating system itself (see Be aware of general security problems, Section 2.2.
Securing Debian Manual2.99 18 April 2004Wed, 3 Mar 2004 09:18:54 +0100