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<title>Securing Debian Manual - Before you begin</title>
<link href="index.en.html" rel="start">
<link href="ch1.en.html" rel="prev">
<link href="ch3.en.html" rel="next">
<link href="index.en.html#contents" rel="contents">
<link href="index.en.html#copyright" rel="copyright">
<link href="ch1.en.html" rel="chapter" title="1 Introduction">
<link href="ch2.en.html" rel="chapter" title="2 Before you begin">
<link href="ch3.en.html" rel="chapter" title="3 Before and during the installation">
<link href="ch4.en.html" rel="chapter" title="4 After installation">
<link href="ch-sec-services.en.html" rel="chapter" title="5 Securing services running on your system">
<link href="ch-automatic-harden.en.html" rel="chapter" title="6 Automatic hardening of Debian systems">
<link href="ch7.en.html" rel="chapter" title="7 Debian Security Infrastructure">
<link href="ch-sec-tools.en.html" rel="chapter" title="8 Security tools in Debian">
<link href="ch9.en.html" rel="chapter" title="9 Developer's Best Practices for OS Security">
<link href="ch10.en.html" rel="chapter" title="10 Before the compromise">
<link href="ch-after-compromise.en.html" rel="chapter" title="11 After the compromise (incident response)">
<link href="ch12.en.html" rel="chapter" title="12 Frequently asked Questions (FAQ)">
<link href="ap-harden-step.en.html" rel="appendix" title="A The hardening process step by step">
<link href="ap-checklist.en.html" rel="appendix" title="B Configuration checklist">
<link href="ap-snort-box.en.html" rel="appendix" title="C Setting up a stand-alone IDS">
<link href="ap-bridge-fw.en.html" rel="appendix" title="D Setting up a bridge firewall">
<link href="ap-bind-chuser.en.html" rel="appendix" title="E Sample script to change the default Bind installation.">
<link href="ap-fw-security-update.en.html" rel="appendix" title="F Security update protected by a firewall">
<link href="ap-chroot-ssh-env.en.html" rel="appendix" title="G <code>Chroot</code> environment for <code>SSH</code>">
<link href="ap-chroot-apache-env.en.html" rel="appendix" title="H <code>Chroot</code> environment for <code>Apache</code>">
<link href="ch1.en.html#s-authors" rel="section" title="1.1 Authors">
<link href="ch1.en.html#s1.2" rel="section" title="1.2 Where to get the manual (and available formats)">
<link href="ch1.en.html#s1.3" rel="section" title="1.3 Organizational notes/feedback">
<link href="ch1.en.html#s1.4" rel="section" title="1.4 Prior knowledge">
<link href="ch1.en.html#s1.5" rel="section" title="1.5 Things that need to be written (FIXME/TODO)">
<link href="ch1.en.html#s-changelog" rel="section" title="1.6 Changelog/History">
<link href="ch1.en.html#s-credits" rel="section" title="1.7 Credits and thanks!">
<link href="ch2.en.html#s2.1" rel="section" title="2.1 What do you want this system for?">
<link href="ch2.en.html#s-references" rel="section" title="2.2 Be aware of general security problems">
<link href="ch2.en.html#s2.3" rel="section" title="2.3 How does Debian handle security?">
<link href="ch3.en.html#s-bios-passwd" rel="section" title="3.1 Choose a BIOS password">
<link href="ch3.en.html#s3.2" rel="section" title="3.2 Partitioning the system">
<link href="ch3.en.html#s3.3" rel="section" title="3.3 Do not plug to the Internet until ready">
<link href="ch3.en.html#s3.4" rel="section" title="3.4 Set a root password">
<link href="ch3.en.html#s3.5" rel="section" title="3.5 Activate shadow passwords and MD5 passwords">
<link href="ch3.en.html#s3.6" rel="section" title="3.6 Run the minimum number of services required">
<link href="ch3.en.html#s3.7" rel="section" title="3.7 Install the minimum amount of software required">
<link href="ch3.en.html#s3.8" rel="section" title="3.8 Read the Debian security mailing lists">
<link href="ch4.en.html#s-debian-sec-announce" rel="section" title="4.1 Subscribe to the Debian Security Announce mailing list">
<link href="ch4.en.html#s-security-update" rel="section" title="4.2 Execute a security update">
<link href="ch4.en.html#s-bios-boot" rel="section" title="4.3 Change the BIOS (again)">
<link href="ch4.en.html#s-lilo-passwd" rel="section" title="4.4 Set a LILO or GRUB password">
<link href="ch4.en.html#s-kernel-initramfs-prompt" rel="section" title="4.5 Disable root prompt on the initramfs">
<link href="ch4.en.html#s-kernel-root-prompt" rel="section" title="4.6 Remove root prompt on the kernel">
<link href="ch4.en.html#s-restrict-console-login" rel="section" title="4.7 Restricting console login access">
<link href="ch4.en.html#s-restrict-reboots" rel="section" title="4.8 Restricting system reboots through the console">
<link href="ch4.en.html#s4.9" rel="section" title="4.9 Mounting partitions the right way">
<link href="ch4.en.html#s4.10" rel="section" title="4.10 Providing secure user access">
<link href="ch4.en.html#s-tcpwrappers" rel="section" title="4.11 Using tcpwrappers">
<link href="ch4.en.html#s-log-alerts" rel="section" title="4.12 The importance of logs and alerts">
<link href="ch4.en.html#s-kernel-patches" rel="section" title="4.13 Adding kernel patches">
<link href="ch4.en.html#s4.14" rel="section" title="4.14 Protecting against buffer overflows">
<link href="ch4.en.html#s4.15" rel="section" title="4.15 Secure file transfers">
<link href="ch4.en.html#s4.16" rel="section" title="4.16 File system limits and control">
<link href="ch4.en.html#s-network-secure" rel="section" title="4.17 Securing network access">
<link href="ch4.en.html#s-snapshot" rel="section" title="4.18 Taking a snapshot of the system">
<link href="ch4.en.html#s4.19" rel="section" title="4.19 Other recommendations">
<link href="ch-sec-services.en.html#s5.1" rel="section" title="5.1 Securing ssh">
<link href="ch-sec-services.en.html#s5.2" rel="section" title="5.2 Securing Squid">
<link href="ch-sec-services.en.html#s-ftp-secure" rel="section" title="5.3 Securing FTP">
<link href="ch-sec-services.en.html#s5.4" rel="section" title="5.4 Securing access to the X Window System">
<link href="ch-sec-services.en.html#s5.5" rel="section" title="5.5 Securing printing access (the lpd and lprng issue)">
<link href="ch-sec-services.en.html#s5.6" rel="section" title="5.6 Securing the mail service">
<link href="ch-sec-services.en.html#s-sec-bind" rel="section" title="5.7 Securing BIND">
<link href="ch-sec-services.en.html#s5.8" rel="section" title="5.8 Securing Apache">
<link href="ch-sec-services.en.html#s5.9" rel="section" title="5.9 Securing finger">
<link href="ch-sec-services.en.html#s-chroot" rel="section" title="5.10 General chroot and suid paranoia">
<link href="ch-sec-services.en.html#s5.11" rel="section" title="5.11 General cleartext password paranoia">
<link href="ch-sec-services.en.html#s5.12" rel="section" title="5.12 Disabling NIS">
<link href="ch-sec-services.en.html#s-rpc" rel="section" title="5.13 Securing RPC services">
<link href="ch-sec-services.en.html#s-firewall-setup" rel="section" title="5.14 Adding firewall capabilities">
<link href="ch-automatic-harden.en.html#s6.1" rel="section" title="6.1 Harden">
<link href="ch-automatic-harden.en.html#s6.2" rel="section" title="6.2 Bastille Linux">
<link href="ch7.en.html#s-debian-sec-team" rel="section" title="7.1 The Debian Security Team">
<link href="ch7.en.html#s-dsa" rel="section" title="7.2 Debian Security Advisories">
<link href="ch7.en.html#s7.3" rel="section" title="7.3 Security Tracker">
<link href="ch7.en.html#s7.4" rel="section" title="7.4 Debian Security Build Infrastructure">
<link href="ch7.en.html#s-deb-pack-sign" rel="section" title="7.5 Package signing in Debian">
<link href="ch-sec-tools.en.html#s-vuln-asses" rel="section" title="8.1 Remote vulnerability assessment tools">
<link href="ch-sec-tools.en.html#s8.2" rel="section" title="8.2 Network scanner tools">
<link href="ch-sec-tools.en.html#s8.3" rel="section" title="8.3 Internal audits">
<link href="ch-sec-tools.en.html#s8.4" rel="section" title="8.4 Auditing source code">
<link href="ch-sec-tools.en.html#s-vpn" rel="section" title="8.5 Virtual Private Networks">
<link href="ch-sec-tools.en.html#s8.6" rel="section" title="8.6 Public Key Infrastructure (PKI)">
<link href="ch-sec-tools.en.html#s8.7" rel="section" title="8.7 SSL Infrastructure">
<link href="ch-sec-tools.en.html#s8.8" rel="section" title="8.8 Antivirus tools">
<link href="ch-sec-tools.en.html#s-gpg-agent" rel="section" title="8.9 GPG agent">
<link href="ch9.en.html#s-bpp-devel-design" rel="section" title="9.1 Best practices for security review and design">
<link href="ch9.en.html#s-bpp-lower-privs" rel="section" title="9.2 Creating users and groups for software daemons">
<link href="ch10.en.html#s-keep-secure" rel="section" title="10.1 Keep your system secure">
<link href="ch10.en.html#s-periodic-integrity" rel="section" title="10.2 Do periodic integrity checks">
<link href="ch10.en.html#s-intrusion-detect" rel="section" title="10.3 Set up Intrusion Detection">
<link href="ch10.en.html#s10.4" rel="section" title="10.4 Avoiding root-kits">
<link href="ch10.en.html#s10.5" rel="section" title="10.5 Genius/Paranoia Ideas &mdash; what you could do">
<link href="ch-after-compromise.en.html#s11.1" rel="section" title="11.1 General behavior">
<link href="ch-after-compromise.en.html#s11.2" rel="section" title="11.2 Backing up the system">
<link href="ch-after-compromise.en.html#s11.3" rel="section" title="11.3 Contact your local CERT">
<link href="ch-after-compromise.en.html#s11.4" rel="section" title="11.4 Forensic analysis">
<link href="ch12.en.html#s12.1" rel="section" title="12.1 Security in the Debian operating system">
<link href="ch12.en.html#s-vulnerable-system" rel="section" title="12.2 My system is vulnerable! (Are you sure?)">
<link href="ch12.en.html#s-debian-sec-team-faq" rel="section" title="12.3 Questions regarding the Debian security team">
<link href="ap-bridge-fw.en.html#sD.1" rel="section" title="D.1 A bridge providing NAT and firewall capabilities">
<link href="ap-bridge-fw.en.html#sD.2" rel="section" title="D.2 A bridge providing firewall capabilities">
<link href="ap-bridge-fw.en.html#sD.3" rel="section" title="D.3 Basic IPtables rules">
<link href="ap-chroot-ssh-env.en.html#sG.1" rel="section" title="G.1 Chrooting the ssh users">
<link href="ap-chroot-ssh-env.en.html#sG.2" rel="section" title="G.2 Chrooting the ssh server">
<link href="ap-chroot-apache-env.en.html#sH.1" rel="section" title="H.1 Introduction">
<link href="ap-chroot-apache-env.en.html#sH.2" rel="section" title="H.2 Installing the server">
<link href="ap-chroot-apache-env.en.html#sH.3" rel="section" title="H.3 See also">
<link href="ch1.en.html#s1.6.1" rel="subsection" title="1.6.1 Version 3.16 (March 2011)">
<link href="ch1.en.html#s1.6.2" rel="subsection" title="1.6.2 Version 3.15 (December 2010)">
<link href="ch1.en.html#s1.6.3" rel="subsection" title="1.6.3 Version 3.14 (March 2009)">
<link href="ch1.en.html#s1.6.4" rel="subsection" title="1.6.4 Version 3.13 (Februrary 2008)">
<link href="ch1.en.html#s1.6.5" rel="subsection" title="1.6.5 Version 3.12 (August 2007)">
<link href="ch1.en.html#s1.6.6" rel="subsection" title="1.6.6 Version 3.11 (January 2007)">
<link href="ch1.en.html#s1.6.7" rel="subsection" title="1.6.7 Version 3.10 (November 2006)">
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<link href="ch1.en.html#s1.6.13" rel="subsection" title="1.6.13 Version 3.4 (August-September 2005)">
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<link href="ch1.en.html#s1.6.48" rel="subsection" title="1.6.48 Version 1.9">
<link href="ch1.en.html#s1.6.49" rel="subsection" title="1.6.49 Version 1.8">
<link href="ch1.en.html#s1.6.50" rel="subsection" title="1.6.50 Version 1.7">
<link href="ch1.en.html#s1.6.51" rel="subsection" title="1.6.51 Version 1.6">
<link href="ch1.en.html#s1.6.52" rel="subsection" title="1.6.52 Version 1.5">
<link href="ch1.en.html#s1.6.53" rel="subsection" title="1.6.53 Version 1.4">
<link href="ch1.en.html#s1.6.54" rel="subsection" title="1.6.54 Version 1.3">
<link href="ch1.en.html#s1.6.55" rel="subsection" title="1.6.55 Version 1.2">
<link href="ch1.en.html#s1.6.56" rel="subsection" title="1.6.56 Version 1.1">
<link href="ch1.en.html#s1.6.57" rel="subsection" title="1.6.57 Version 1.0">
<link href="ch3.en.html#s3.2.1" rel="subsection" title="3.2.1 Choose an intelligent partition scheme">
<link href="ch3.en.html#s3.2.1.1" rel="subsection" title="3.2.1.1 Selecting the appropriate file systems">
<link href="ch3.en.html#s-disableserv" rel="subsection" title="3.6.1 Disabling daemon services">
<link href="ch3.en.html#s-inetd" rel="subsection" title="3.6.2 Disabling <code>inetd</code> or its services">
<link href="ch3.en.html#s3.7.1" rel="subsection" title="3.7.1 Removing Perl">
<link href="ch4.en.html#s-lib-security-update" rel="subsection" title="4.2.1 Security update of libraries">
<link href="ch4.en.html#s-kernel-security-update" rel="subsection" title="4.2.2 Security update of the kernel">
<link href="ch4.en.html#s4.9.1" rel="subsection" title="4.9.1 Setting <code>/tmp</code> noexec">
<link href="ch4.en.html#s4.9.2" rel="subsection" title="4.9.2 Setting /usr read-only">
<link href="ch4.en.html#s-auth-pam" rel="subsection" title="4.10.1 User authentication: PAM">
<link href="ch4.en.html#s-user-limits" rel="subsection" title="4.10.2 Limiting resource usage: the <code>limits.conf</code> file">
<link href="ch4.en.html#s4.10.3" rel="subsection" title="4.10.3 User login actions: edit <code>/etc/login.defs</code>">
<link href="ch4.en.html#s4.10.4" rel="subsection" title="4.10.4 Restricting ftp: editing <code>/etc/ftpusers</code>">
<link href="ch4.en.html#s4.10.5" rel="subsection" title="4.10.5 Using su">
<link href="ch4.en.html#s4.10.6" rel="subsection" title="4.10.6 Using sudo">
<link href="ch4.en.html#s4.10.7" rel="subsection" title="4.10.7 Disallow remote administrative access">
<link href="ch4.en.html#s-user-restrict" rel="subsection" title="4.10.8 Restricting users's access">
<link href="ch4.en.html#s4.10.9" rel="subsection" title="4.10.9 User auditing">
<link href="ch4.en.html#s4.10.9.1" rel="subsection" title="4.10.9.1 Input and output audit with script">
<link href="ch4.en.html#s4.10.9.2" rel="subsection" title="4.10.9.2 Using the shell history file">
<link href="ch4.en.html#s4.10.9.3" rel="subsection" title="4.10.9.3 Complete user audit with accounting utilities">
<link href="ch4.en.html#s4.10.9.4" rel="subsection" title="4.10.9.4 Other user auditing methods">
<link href="ch4.en.html#s4.10.10" rel="subsection" title="4.10.10 Reviewing user profiles">
<link href="ch4.en.html#s4.10.11" rel="subsection" title="4.10.11 Setting users umasks">
<link href="ch4.en.html#s4.10.12" rel="subsection" title="4.10.12 Limiting what users can see/access">
<link href="ch4.en.html#s-limit-user-perm" rel="subsection" title="4.10.12.1 Limiting access to other user's information">
<link href="ch4.en.html#s-user-pwgen" rel="subsection" title="4.10.13 Generating user passwords">
<link href="ch4.en.html#s4.10.14" rel="subsection" title="4.10.14 Checking user passwords">
<link href="ch4.en.html#s-idle-logoff" rel="subsection" title="4.10.15 Logging off idle users">
<link href="ch4.en.html#s-custom-logcheck" rel="subsection" title="4.12.1 Using and customizing <code>logcheck</code>">
<link href="ch4.en.html#s4.12.2" rel="subsection" title="4.12.2 Configuring where alerts are sent">
<link href="ch4.en.html#s4.12.3" rel="subsection" title="4.12.3 Using a loghost">
<link href="ch4.en.html#s4.12.4" rel="subsection" title="4.12.4 Log file permissions">
<link href="ch4.en.html#s4.14.1" rel="subsection" title="4.14.1 Kernel patch protection for buffer overflows">
<link href="ch4.en.html#s4.14.2" rel="subsection" title="4.14.2 Testing programs for overflows">
<link href="ch4.en.html#s4.16.1" rel="subsection" title="4.16.1 Using quotas">
<link href="ch4.en.html#s-ext2attr" rel="subsection" title="4.16.2 The ext2 filesystem specific attributes (chattr/lsattr)">
<link href="ch4.en.html#s-check-integ" rel="subsection" title="4.16.3 Checking file system integrity">
<link href="ch4.en.html#s4.16.4" rel="subsection" title="4.16.4 Setting up setuid check">
<link href="ch4.en.html#s-kernel-conf" rel="subsection" title="4.17.1 Configuring kernel network features">
<link href="ch4.en.html#s-tcp-syncookies" rel="subsection" title="4.17.2 Configuring syncookies">
<link href="ch4.en.html#s-net-harden" rel="subsection" title="4.17.3 Securing the network on boot-time">
<link href="ch4.en.html#s-kernel-fw" rel="subsection" title="4.17.4 Configuring firewall features">
<link href="ch4.en.html#s-limit-bindaddr" rel="subsection" title="4.17.5 Disabling weak-end hosts issues">
<link href="ch4.en.html#s4.17.6" rel="subsection" title="4.17.6 Protecting against ARP attacks">
<link href="ch4.en.html#s4.19.1" rel="subsection" title="4.19.1 Do not use software depending on svgalib">
<link href="ch-sec-services.en.html#s-ssh-chroot" rel="subsection" title="5.1.1 Chrooting ssh">
<link href="ch-sec-services.en.html#s5.1.2" rel="subsection" title="5.1.2 Ssh clients">
<link href="ch-sec-services.en.html#s5.1.3" rel="subsection" title="5.1.3 Disallowing file transfers">
<link href="ch-sec-services.en.html#s-ssh-only-file" rel="subsection" title="5.1.4 Restricing access to file transfer only">
<link href="ch-sec-services.en.html#s5.4.1" rel="subsection" title="5.4.1 Check your display manager">
<link href="ch-sec-services.en.html#s5.6.1" rel="subsection" title="5.6.1 Configuring a Nullmailer">
<link href="ch-sec-services.en.html#s5.6.2" rel="subsection" title="5.6.2 Providing secure access to mailboxes">
<link href="ch-sec-services.en.html#s5.6.3" rel="subsection" title="5.6.3 Receiving mail securely">
<link href="ch-sec-services.en.html#s-configure-bind" rel="subsection" title="5.7.1 Bind configuration to avoid misuse">
<link href="ch-sec-services.en.html#s-user-bind" rel="subsection" title="5.7.2 Changing BIND's user">
<link href="ch-sec-services.en.html#s-chroot-bind" rel="subsection" title="5.7.3 Chrooting the name server">
<link href="ch-sec-services.en.html#s5.8.1" rel="subsection" title="5.8.1 Disabling users from publishing web contents">
<link href="ch-sec-services.en.html#s5.8.2" rel="subsection" title="5.8.2 Logfiles permissions">
<link href="ch-sec-services.en.html#s5.8.3" rel="subsection" title="5.8.3 Published web files">
<link href="ch-sec-services.en.html#s-auto-chroot" rel="subsection" title="5.10.1 Making chrooted environments automatically">
<link href="ch-sec-services.en.html#s5.13.1" rel="subsection" title="5.13.1 Disabling RPC services completely">
<link href="ch-sec-services.en.html#s5.13.2" rel="subsection" title="5.13.2 Limiting access to RPC services">
<link href="ch-sec-services.en.html#s5.14.1" rel="subsection" title="5.14.1 Firewalling the local system">
<link href="ch-sec-services.en.html#s5.14.2" rel="subsection" title="5.14.2 Using a firewall to protect other systems">
<link href="ch-sec-services.en.html#s5.14.3" rel="subsection" title="5.14.3 Setting up a firewall">
<link href="ch-sec-services.en.html#s-firewall-pack" rel="subsection" title="5.14.3.1 Using firewall packages">
<link href="ch-sec-services.en.html#s5.14.3.2" rel="subsection" title="5.14.3.2 Manual init.d configuration">
<link href="ch-sec-services.en.html#s5.14.3.3" rel="subsection" title="5.14.3.3 Configuring firewall rules through <code>ifup</code>">
<link href="ch-sec-services.en.html#s5.14.3.4" rel="subsection" title="5.14.3.4 Testing your firewall configuration">
<link href="ch7.en.html#s-crossreference" rel="subsection" title="7.2.1 Vulnerability cross references">
<link href="ch7.en.html#s-cve-compatible" rel="subsection" title="7.2.2 CVE compatibility">
<link href="ch7.en.html#s7.4.1" rel="subsection" title="7.4.1 Developer's guide to security updates">
<link href="ch7.en.html#s7.5.1" rel="subsection" title="7.5.1 The current scheme for package signature checks">
<link href="ch7.en.html#s-apt-0.6" rel="subsection" title="7.5.2 Secure apt">
<link href="ch7.en.html#s-check-releases" rel="subsection" title="7.5.3 Per distribution release check">
<link href="ch7.en.html#s7.5.3.1" rel="subsection" title="7.5.3.1 Basic concepts">
<link href="ch7.en.html#s7.5.3.2" rel="subsection" title="7.5.3.2 <code>Release</code> checksums">
<link href="ch7.en.html#s7.5.3.3" rel="subsection" title="7.5.3.3 Verification of the <code>Release</code> file">
<link href="ch7.en.html#s7.5.3.4" rel="subsection" title="7.5.3.4 Check of <code>Release.gpg</code> by <code>apt</code>">
<link href="ch7.en.html#s7.5.3.5" rel="subsection" title="7.5.3.5 How to tell apt what to trust">
<link href="ch7.en.html#s7.5.3.6" rel="subsection" title="7.5.3.6 Finding the key for a repository">
<link href="ch7.en.html#s-secure-apt-add-key" rel="subsection" title="7.5.3.7 Safely adding a key">
<link href="ch7.en.html#s7.5.3.8" rel="subsection" title="7.5.3.8 Verifying key integrity">
<link href="ch7.en.html#s7.5.3.9" rel="subsection" title="7.5.3.9 Debian archive key yearly rotation">
<link href="ch7.en.html#s7.5.3.10" rel="subsection" title="7.5.3.10 Known release checking problems">
<link href="ch7.en.html#s-manual-check-releases" rel="subsection" title="7.5.3.11 Manual per distribution release check">
<link href="ch7.en.html#s-check-non-debian-releases" rel="subsection" title="7.5.4 Release check of non Debian sources">
<link href="ch7.en.html#s-check-pkg-sign" rel="subsection" title="7.5.5 Alternative per-package signing scheme">
<link href="ch-sec-tools.en.html#s8.5.1" rel="subsection" title="8.5.1 Point to Point tunneling">
<link href="ch10.en.html#s-track-vulns" rel="subsection" title="10.1.1 Tracking security vulnerabilities">
<link href="ch10.en.html#s-keep-up-to-date" rel="subsection" title="10.1.2 Continuously update the system">
<link href="ch10.en.html#s10.1.2.1" rel="subsection" title="10.1.2.1 Manually checking which security updates are available">
<link href="ch10.en.html#s-update-desktop" rel="subsection" title="10.1.2.2 Checking for updates at the Desktop">
<link href="ch10.en.html#s-cron-apt" rel="subsection" title="10.1.2.3 Automatically checking for updates with cron-apt">
<link href="ch10.en.html#s-debsecan" rel="subsection" title="10.1.2.4 Automatically checking for security issues with debsecan">
<link href="ch10.en.html#s10.1.2.5" rel="subsection" title="10.1.2.5 Other methods for security updates">
<link href="ch10.en.html#s10.1.3" rel="subsection" title="10.1.3 Avoid using the unstable branch">
<link href="ch10.en.html#s-security-support-testing" rel="subsection" title="10.1.4 Security support for the testing branch">
<link href="ch10.en.html#s10.1.5" rel="subsection" title="10.1.5 Automatic updates in a Debian GNU/Linux system">
<link href="ch10.en.html#s10.3.1" rel="subsection" title="10.3.1 Network based intrusion detection">
<link href="ch10.en.html#s10.3.2" rel="subsection" title="10.3.2 Host based intrusion detection">
<link href="ch10.en.html#s-LKM" rel="subsection" title="10.4.1 Loadable Kernel Modules (LKM)">
<link href="ch10.en.html#s10.4.2" rel="subsection" title="10.4.2 Detecting root-kits">
<link href="ch10.en.html#s-proactive" rel="subsection" title="10.4.2.1 Proactive defense">
<link href="ch10.en.html#s10.4.2.2" rel="subsection" title="10.4.2.2 Reactive defense">
<link href="ch10.en.html#s10.5.1" rel="subsection" title="10.5.1 Building a honeypot">
<link href="ch-after-compromise.en.html#s11.4.1" rel="subsection" title="11.4.1 Analysis of malware">
<link href="ch12.en.html#s12.1.1" rel="subsection" title="12.1.1 Is Debian more secure than X?">
<link href="ch12.en.html#s12.1.1.1" rel="subsection" title="12.1.1.1 Is Debian more secure than other Linux distributions (such as Red Hat, SuSE...)?">
<link href="ch12.en.html#s12.1.2" rel="subsection" title="12.1.2 There are many Debian bugs in Bugtraq. Does this mean that it is very vulnerable?">
<link href="ch12.en.html#s12.1.3" rel="subsection" title="12.1.3 Does Debian have any certification related to security?">
<link href="ch12.en.html#s12.1.4" rel="subsection" title="12.1.4 Are there any hardening programs for Debian?">
<link href="ch12.en.html#s12.1.5" rel="subsection" title="12.1.5 I want to run XYZ service, which one should I choose?">
<link href="ch12.en.html#s12.1.6" rel="subsection" title="12.1.6 How can I make service XYZ more secure in Debian?">
<link href="ch12.en.html#s12.1.7" rel="subsection" title="12.1.7 How can I remove all the banners for services?">
<link href="ch12.en.html#s12.1.8" rel="subsection" title="12.1.8 Are all Debian packages safe?">
<link href="ch12.en.html#s12.1.9" rel="subsection" title="12.1.9 Why are some log files/configuration files world-readable, isn't this insecure?">
<link href="ch12.en.html#s12.1.10" rel="subsection" title="12.1.10 Why does /root/ (or UserX) have 755 permissions?">
<link href="ch12.en.html#s12.1.11" rel="subsection" title="12.1.11 After installing a grsec/firewall, I started receiving many console messages! How do I remove them?">
<link href="ch12.en.html#s-faq-os-users" rel="subsection" title="12.1.12 Operating system users and groups">
<link href="ch12.en.html#s12.1.12.1" rel="subsection" title="12.1.12.1 Are all system users necessary?">
<link href="ch12.en.html#s12.1.12.2" rel="subsection" title="12.1.12.2 I removed a system user! How can I recover?">
<link href="ch12.en.html#s12.1.12.3" rel="subsection" title="12.1.12.3 What is the difference between the adm and the staff group?">
<link href="ch12.en.html#s12.1.13" rel="subsection" title="12.1.13 Why is there a new group when I add a new user? (or Why does Debian give each user one group?)">
<link href="ch12.en.html#s12.1.14" rel="subsection" title="12.1.14 Questions regarding services and open ports">
<link href="ch12.en.html#s12.1.14.1" rel="subsection" title="12.1.14.1 Why are all services activated upon installation?">
<link href="ch12.en.html#s12.1.14.2" rel="subsection" title="12.1.14.2 Can I remove <code>inetd</code>?">
<link href="ch12.en.html#s12.1.14.3" rel="subsection" title="12.1.14.3 Why do I have port 111 open?">
<link href="ch12.en.html#s12.1.14.4" rel="subsection" title="12.1.14.4 What use is <code>identd</code> (port 113) for?">
<link href="ch12.en.html#s12.1.14.5" rel="subsection" title="12.1.14.5 I have services using port 1 and 6, what are they and how can I remove them?">
<link href="ch12.en.html#s12.1.14.6" rel="subsection" title="12.1.14.6 I found the port XYZ open, can I close it?">
<link href="ch12.en.html#s12.1.14.7" rel="subsection" title="12.1.14.7 Will removing services from <code>/etc/services</code> help secure my box?">
<link href="ch12.en.html#s12.1.15" rel="subsection" title="12.1.15 Common security issues">
<link href="ch12.en.html#s12.1.15.1" rel="subsection" title="12.1.15.1 I have lost my password and cannot access the system!">
<link href="ch12.en.html#s12.1.16" rel="subsection" title="12.1.16 How do I accomplish setting up a service for my users without giving out shell accounts?">
<link href="ch12.en.html#s-vulnasses-false-positive" rel="subsection" title="12.2.1 Vulnerability assessment scanner X says my Debian system is vulnerable!">
<link href="ch12.en.html#s12.2.2" rel="subsection" title="12.2.2 I've seen an attack in my system's logs. Is my system compromised?">
<link href="ch12.en.html#s12.2.3" rel="subsection" title="12.2.3 I have found strange 'MARK' lines in my logs: Am I compromised?">
<link href="ch12.en.html#s12.2.4" rel="subsection" title="12.2.4 I found users using 'su' in my logs: Am I compromised?">
<link href="ch12.en.html#s12.2.5" rel="subsection" title="12.2.5 I have found 'possible SYN flooding' in my logs: Am I under attack?">
<link href="ch12.en.html#s12.2.6" rel="subsection" title="12.2.6 I have found strange root sessions in my logs: Am I compromised?">
<link href="ch12.en.html#s12.2.7" rel="subsection" title="12.2.7 I have suffered a break-in, what do I do?">
<link href="ch12.en.html#s12.2.8" rel="subsection" title="12.2.8 How can I trace an attack?">
<link href="ch12.en.html#s12.2.9" rel="subsection" title="12.2.9 Program X in Debian is vulnerable, what do I do?">
<link href="ch12.en.html#s-version-backport" rel="subsection" title="12.2.10 The version number for a package indicates that I am still running a vulnerable version!">
<link href="ch12.en.html#s12.2.11" rel="subsection" title="12.2.11 Specific software">
<link href="ch12.en.html#s12.2.11.1" rel="subsection" title="12.2.11.1 <code>proftpd</code> is vulnerable to a Denial of Service attack.">
<link href="ch12.en.html#s12.2.11.2" rel="subsection" title="12.2.11.2 After installing <code>portsentry</code>, there are a lot of ports open.">
<link href="ch12.en.html#s12.3.1" rel="subsection" title="12.3.1 What is a Debian Security Advisory (DSA)?">
<link href="ch12.en.html#s12.3.2" rel="subsection" title="12.3.2 The signature on Debian advisories does not verify correctly!">
<link href="ch12.en.html#s12.3.3" rel="subsection" title="12.3.3 How is security handled in Debian?">
<link href="ch12.en.html#s12.3.4" rel="subsection" title="12.3.4 Why are you fiddling with an old version of that package?">
<link href="ch12.en.html#s12.3.5" rel="subsection" title="12.3.5 What is the policy for a fixed package to appear in security.debian.org?">
<link href="ch12.en.html#s12.3.6" rel="subsection" title="12.3.6 What does &quot;local (remote)&quot; mean?">
<link href="ch12.en.html#s12.3.7" rel="subsection" title="12.3.7 The version number for a package indicates that I am still running a vulnerable version!">
<link href="ch12.en.html#s-sec-unstable" rel="subsection" title="12.3.8 How is security handled for <samp>testing</samp> and <samp>unstable</samp>?">
<link href="ch12.en.html#s-sec-older" rel="subsection" title="12.3.9 I use an older version of Debian, is it supported by the Debian Security Team?">
<link href="ch12.en.html#s12.3.10" rel="subsection" title="12.3.10 How does <em>testing</em> get security updates?">
<link href="ch12.en.html#s12.3.11" rel="subsection" title="12.3.11 How is security handled for contrib and non-free?">
<link href="ch12.en.html#s12.3.12" rel="subsection" title="12.3.12 Why are there no official mirrors for security.debian.org?">
<link href="ch12.en.html#s12.3.13" rel="subsection" title="12.3.13 I've seen DSA 100 and DSA 102, now where is DSA 101?">
<link href="ch12.en.html#s12.3.14" rel="subsection" title="12.3.14 I tried to download a package listed in one of the security advisories, but I got a `file not found' error.">
<link href="ch12.en.html#s12.3.15" rel="subsection" title="12.3.15 How can I reach the security team?">
<link href="ch12.en.html#s12.3.16" rel="subsection" title="12.3.16 What difference is there between security@debian.org and debian-security@lists.debian.org?">
<link href="ch12.en.html#s12.3.17" rel="subsection" title="12.3.17 I guess I found a security problem, what should I do?">
<link href="ch12.en.html#s12.3.18" rel="subsection" title="12.3.18 How can I contribute to the Debian security team?">
<link href="ch12.en.html#s12.3.19" rel="subsection" title="12.3.19 Who is the Security Team composed of?">
<link href="ch12.en.html#s12.3.20" rel="subsection" title="12.3.20 Does the Debian Security team check every new package in Debian?">
<link href="ch12.en.html#s12.3.21" rel="subsection" title="12.3.21 How much time will it take Debian to fix vulnerability XXXX?">
<link href="ch12.en.html#s12.3.22" rel="subsection" title="12.3.22 How long will security updates be provided?">
<link href="ch12.en.html#s12.3.23" rel="subsection" title="12.3.23 How can I check the integrity of packages?">
<link href="ch12.en.html#s12.3.24" rel="subsection" title="12.3.24 What to do if a random package breaks after a security update?">
<link href="ap-chroot-ssh-env.en.html#sG.1.1" rel="subsection" title="G.1.1 Using <code>libpam-chroot</code>">
<link href="ap-chroot-ssh-env.en.html#sG.1.2" rel="subsection" title="G.1.2 Patching the <code>ssh</code> server">
<link href="ap-chroot-ssh-env.en.html#sG.2.1" rel="subsection" title="G.2.1 Setup a minimal system (the really easy way)">
<link href="ap-chroot-ssh-env.en.html#sG.2.2" rel="subsection" title="G.2.2 Automatically making the environment (the easy way)">
<link href="ap-chroot-ssh-env.en.html#sG.2.3" rel="subsection" title="G.2.3 Manually creating the environment (the hard way)">
<link href="ap-chroot-apache-env.en.html#sH.1.1" rel="subsection" title="H.1.1 Licensing">
</head>
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<p><a name="ch2"></a></p>
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[ <a href="index.en.html#contents">Contents</a> ]
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</p>
<hr>
<h1>
Securing Debian Manual
<br>Chapter 2 - Before you begin
</h1>
<hr>
<h2><a name="s2.1"></a>2.1 What do you want this system for?</h2>
<p>
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.
</p>
<p>
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:
</p>
<ul>
<li>
<p>
Decide which services you need and limit your system to those. This includes
deactivating/uninstalling unneeded services, and adding firewall-like filters,
or tcpwrappers.
</p>
</li>
</ul>
<ul>
<li>
<p>
Limit users and permissions in your system.
</p>
</li>
</ul>
<ul>
<li>
<p>
Harden offered services so that, in the event of a service compromise, the
impact to your system is minimized.
</p>
</li>
</ul>
<ul>
<li>
<p>
Use appropriate tools to guarantee that unauthorized use is detected so that
you can take appropriate measures.
</p>
</li>
</ul>
<hr>
<h2><a name="s-references"></a>2.2 Be aware of general security problems</h2>
<p>
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).
</p>
<p>
Some useful documents include:
</p>
<ul>
<li>
<p>
The <code><a href="http://www.tldp.org/HOWTO/Security-HOWTO/">Linux Security
HOWTO</a></code> (also available at <code><a
href="http://www.linuxsecurity.com/docs/LDP/Security-HOWTO.html">LinuxSecurity</a></code>)
is one of the best references regarding general Linux security.
</p>
</li>
</ul>
<ul>
<li>
<p>
The <code><a
href="http://www.tldp.org/HOWTO/Security-Quickstart-HOWTO/">Security
Quick-Start HOWTO for Linux</a></code> is also a very good starting point for
novice users (both to Linux and security).
</p>
</li>
</ul>
<ul>
<li>
<p>
The <code><a href="http://seifried.org/lasg/">Linux Security Administrator's
Guide</a></code> 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. [<a
href="footnotes.en.html#f1" name="fr1">1</a>]
</p>
</li>
</ul>
<ul>
<li>
<p>
Kurt Seifried's <code><a
href="http://seifried.org/security/os/linux/20020324-securing-linux-step-by-step.html">Securing
Linux Step by Step</a></code>.
</p>
</li>
</ul>
<ul>
<li>
<p>
In <code><a
href="http://www.tldp.org/links/p_books.html#securing_linux">Securing and
Optimizing Linux: RedHat Edition</a></code> you can find a similar document to
this manual but related to Red Hat, some of the issues are not
distribution-specific and also apply to Debian.
</p>
</li>
</ul>
<ul>
<li>
<p>
Another Red Hat related document is <code><a
href="http://ltp.sourceforge.net/docs/RHEL-EAL3-Configuration-Guide.pdf">EAL3
Evaluated Configuration Guide for Red Hat Enterprise</a></code>.
</p>
</li>
</ul>
<ul>
<li>
<p>
IntersectAlliance has published some documents that can be used as reference
cards on how to harden Linux servers (and their services), the documents are
available at <code><a
href="http://www.intersectalliance.com/projects/index.html">their
site</a></code>.
</p>
</li>
</ul>
<ul>
<li>
<p>
For network administrators, a good reference for building a secure network is
the <code><a
href="http://www.linuxsecurity.com/docs/LDP/Securing-Domain-HOWTO/">Securing
your Domain HOWTO</a></code>.
</p>
</li>
</ul>
<ul>
<li>
<p>
If you want to evaluate the programs you are going to use (or want to build up
some new ones) you should read the <code><a
href="http://www.tldp.org/HOWTO/Secure-Programs-HOWTO/">Secure Programs
HOWTO</a></code> (master copy is available at <code><a
href="http://www.dwheeler.com/secure-programs/">http://www.dwheeler.com/secure-programs/</a></code>,
it includes slides and talks from the author, David Wheeler)
</p>
</li>
</ul>
<ul>
<li>
<p>
If you are considering installing firewall capabilities, you should read the
<code><a href="http://www.tldp.org/HOWTO/Firewall-HOWTO.html">Firewall
HOWTO</a></code> and the <code><a
href="http://www.tldp.org/HOWTO/IPCHAINS-HOWTO.html">IPCHAINS HOWTO</a></code>
(for kernels previous to 2.4).
</p>
</li>
</ul>
<ul>
<li>
<p>
Finally, a good card to keep handy is the <code><a
href="http://www.linuxsecurity.com/docs/QuickRefCard.pdf">Linux Security
ReferenceCard</a></code>.
</p>
</li>
</ul>
<p>
In any case, there is more information regarding the services explained here
(NFS, NIS, SMB...) in many of the HOWTOs of the <code><a
href="http://www.tldp.org/">The Linux Documentation Project</a></code>. Some
of these documents speak on the security side of a given service, so be sure to
take a look there too.
</p>
<p>
The HOWTO documents from the Linux Documentation Project are available in
Debian GNU/Linux through the installation of the <code>doc-linux-text</code>
(text version) or <code>doc-linux-html</code> (HTML version). After
installation these documents will be available at the
<code>/usr/share/doc/HOWTO/en-txt</code> and
<code>/usr/share/doc/HOWTO/en-html</code> directories, respectively.
</p>
<p>
Other recommended Linux books:
</p>
<ul>
<li>
<p>
Maximum Linux Security : A Hacker's Guide to Protecting Your Linux Server and
Network. Anonymous. Paperback - 829 pages. Sams Publishing. ISBN:
0672313413. July 1999.
</p>
</li>
</ul>
<ul>
<li>
<p>
Linux Security By John S. Flowers. New Riders; ISBN: 0735700354. March 1999.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code><a href="http://www.linux.org/books/ISBN_0072127732.html">Hacking Linux
Exposed</a></code> By Brian Hatch. McGraw-Hill Higher Education. ISBN
0072127732. April, 2001
</p>
</li>
</ul>
<p>
Other books (which might be related to general issues regarding UNIX and
security and not Linux specific):
</p>
<ul>
<li>
<p>
<code><a href="http://www.ora.com/catalog/puis/noframes.html">Practical Unix
and Internet Security (2nd Edition)</a></code> Garfinkel, Simpson, and
Spafford, Gene; O'Reilly Associates; ISBN 0-56592-148-8; 1004pp; 1996.
</p>
</li>
</ul>
<ul>
<li>
<p>
Firewalls and Internet Security Cheswick, William R. and Bellovin, Steven M.;
Addison-Wesley; 1994; ISBN 0-201-63357-4; 320pp.
</p>
</li>
</ul>
<p>
Some useful web sites to keep up to date regarding security:
</p>
<ul>
<li>
<p>
<code><a href="http://csrc.nist.gov/fasp/index.html">NIST Security
Guidelines</a></code>.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code><a href="http://www.securityfocus.com">Security Focus</a></code> the
server that hosts the Bugtraq vulnerability database and list, and provides
general security information, news and reports.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code><a href="http://www.linuxsecurity.com/">Linux Security</a></code>.
General information regarding Linux security (tools, news...). Most useful is
the <code><a
href="http://www.linuxsecurity.com/resources/documentation-1.html">main
documentation</a></code> page.
</p>
</li>
</ul>
<ul>
<li>
<p>
<code><a href="http://www.linux-firewall-tools.com/linux/">Linux firewall and
security site</a></code>. General information regarding Linux firewalls and
tools to control and administrate them.
</p>
</li>
</ul>
<hr>
<h2><a name="s2.3"></a>2.3 How does Debian handle security?</h2>
<p>
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:
</p>
<ul>
<li>
<p>
Debian problems are always handled openly, even security related. Security
issues are discussed openly on the debian-security mailing list. Debian
Security Advisories (DSAs) are sent to public mailing lists (both internal and
external) and are published on the public server. As the <code><a
href="http://www.debian.org/social_contract">Debian Social Contract</a></code>
states:
</p>
<p>
<em>We will not hide problems</em>
</p>
<p>
<em>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.</em>
</p>
</li>
</ul>
<ul>
<li>
<p>
Debian follows security issues closely. The security team checks many security
related sources, the most important being <code><a
href="http://www.securityfocus.com/cgi-bin/vulns.pl">Bugtraq</a></code>, on the
lookout for packages with security issues that might be included in Debian.
</p>
</li>
</ul>
<ul>
<li>
<p>
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, testing and unstable releases, including all
architectures.
</p>
</li>
</ul>
<ul>
<li>
<p>
Information regarding security is centralized in a single point, <code><a
href="http://security.debian.org/">http://security.debian.org/</a></code>.
</p>
</li>
</ul>
<ul>
<li>
<p>
Debian is always trying to improve the overall security of the distribution by
starting new projects, such as automatic package signature verification
mechanisms.
</p>
</li>
</ul>
<ul>
<li>
<p>
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.
</p>
</li>
</ul>
<ul>
<li>
<p>
Package maintainers are aware of security issues. This leads to many
&quot;secure by default&quot; 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 operating
systems). In any case, prominent security issues (such as <samp>setuid</samp>
programs) are part of the <code><a
href="http://www.debian.org/doc/debian-policy/">Debian Policy</a></code>.
</p>
</li>
</ul>
<p>
By publishing security information specific to Debian and complementing other
information-security documents related to Debian (see <a
href="#s-references">Be aware of general security problems, Section 2.2</a>),
this document aims to produce better system installations security-wise.
</p>
<hr>
<p>
[ <a href="ch1.en.html">previous</a> ]
[ <a href="index.en.html#contents">Contents</a> ]
[ <a href="ch1.en.html">1</a> ]
[ 2 ]
[ <a href="ch3.en.html">3</a> ]
[ <a href="ch4.en.html">4</a> ]
[ <a href="ch-sec-services.en.html">5</a> ]
[ <a href="ch-automatic-harden.en.html">6</a> ]
[ <a href="ch7.en.html">7</a> ]
[ <a href="ch-sec-tools.en.html">8</a> ]
[ <a href="ch9.en.html">9</a> ]
[ <a href="ch10.en.html">10</a> ]
[ <a href="ch-after-compromise.en.html">11</a> ]
[ <a href="ch12.en.html">12</a> ]
[ <a href="ap-harden-step.en.html">A</a> ]
[ <a href="ap-checklist.en.html">B</a> ]
[ <a href="ap-snort-box.en.html">C</a> ]
[ <a href="ap-bridge-fw.en.html">D</a> ]
[ <a href="ap-bind-chuser.en.html">E</a> ]
[ <a href="ap-fw-security-update.en.html">F</a> ]
[ <a href="ap-chroot-ssh-env.en.html">G</a> ]
[ <a href="ap-chroot-apache-env.en.html">H</a> ]
[ <a href="ch3.en.html">next</a> ]
</p>
<hr>
<p>
Securing Debian Manual
</p>
<address>
Version: 3.13, Sun, 08 Apr 2012 02:48:09 +0000<br>
<br>
Javier Fern&aacute;ndez-Sanguino Pe&ntilde;a <code><a href="mailto:jfs@debian.org">jfs@debian.org</a></code><br>
<a href="ch1.en.html#s-authors">Authors, Section 1.1</a><br>
<br>
</address>
<hr>
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