Securing Debian Manual

Peter Kitson

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Sample Chapter From Securing Debian Manual
     Copyright © Javier Fernández-Sanguino Peña


One of the hardest things about writing security documents is that every case is unique. Two things you have to pay attention to are the threat environment and the security needs of the individual site, host, or network. For instance, the security needs of a home user are completely different from a network in a bank. While the primary threat a home user needs to face is the script kiddie type of cracker, a bank network has to worry about directed attacks. Additionally, the bank has to protect their customer’s data with arithmetic precision. In short, every user has to consider the trade-off between usability and security/paranoia.

Note that this manual only covers issues relating to software. The best software in the world can’t protect you if someone can physically access the machine. You can place it under your desk, or you can place it in a hardened bunker with an army in front of it. Nevertheless the desktop computer can be much more secure (from a software point of view) than a physically protected one if the desktop is configured properly and the software on the protected machine is full of security holes. Obviously, you must consider both issues.

This document just gives an overview of what you can do to increase the security of your Debian GNU/Linux system. If you have read other documents regarding Linux security, you will find that there are common issues which might overlap with this document. However, this document does not try to be the ultimate source of information you will be using, it only tries to adapt this same information so that it is meaningful to a Debian GNU/Linux system. Different distributions do some things in different ways (startup of daemons is one example); here, you will find material which is appropriate for Debian’s procedures and tools.

2.3 How does Debian handle security?

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 problems are always handled openly, even security related. Security issues are discussed openly on the debian-security mailing list. Debian Security Advisories are sent to public mailing lists (both internal and external) and are published on the public server. As the Debian Social Contract ( states:

We will not hide problems

We will keep our entire bug report database open for public view at all times. Reports that people file online will promptly become visible to others.

• Debian follows security issues closely. The security team checks many security related sources, the most important being Bugtraq (, on the lookout for packages with security issues that might be included in Debian.

• Security updates are the first priority. When a security problem arises in a Debian package, the security update is prepared as fast as possible and distributed for our stable and unstable releases, including all architectures.

• Information regarding security is centralized in a single point,

• Debian is always trying to improve the overall security of the distribution by starting new projects, such as automatic package signature verification mechanisms.

• Debian provides a number of useful security related tools for system administration and monitoring. Developers try to tightly integrate these tools with the distribution in order to make them a better suite to enforce local security policies. Tools include: integrity checkers, auditing tools, hardening tools, firewall tools, intrusion detection tools, etc.

• Package maintainers are aware of security issues. This leads to many "secure by default" service installations which could impose certain restrictions on their normal use. Debian does, however, try to balance security and ease of administration - the programs are not de-activated when you install them (as it is the case with say, the BSD family of distributions). In any case, prominent security issues (such as setuid programs) are part of the Debian Policy (

By publishing security information specific to Debian and complementing other informationsecurity documents related to Debian GNU (see ‘Be aware of general security problems’ on page 27), this document aims to produce better system installations security-wise.