linux_hardening.txt

Linux Hardening Points and ideas
License: GNU Free Documentation License - Version 1.3, 3 November 2008 (for details, see LICENSE.txt)
Author: 51x

=========
Debian hardening points for workstations

- While installing, set up LVM with LUKS encryption (/boot cannot be encrypted, you can keep it on a pendrive or a cryptostick)

- Recommended mount options (add "discard" for SSD):
    /home     rw,nodev,nouser,noexec,nosuid
    /tmp      rw,nodev,noexec,nouser,nosuid
    /var/tmp  rw,nodev,noexec,nouser,nosuid
    /var      rw,nodev,nouser,nosuid
    # /var could be noexec too, but it would break apt that way.
    
- Hide processes that the user don't need to see (fstab too)
    proc    /proc    proc    defaults,hidepid=2  0  0

- Configure auto update to run everyday (on Debian "unattended-upgrades", on Ubuntu you can do it with Software Center settings)
    https://wiki.debian.org/UnattendedUpgrades

- Remove unnecessary programs (eg. avahi-daemon and rpcbind)
    netstat -tulnp  # Check listening apps and if not needed remove them
    apt-get remove avahi-daemon # "remove" will keep config files, purge deletes everythin!

- Disable USB Mass Storages if you don't need them
    echo "blacklist usb-storage" | tee -a /etc/modprobe.d/blacklist.conf
    update-initramfs -u

- Use apparmor for stricter privileges.
   # https://wiki.debian.org/AppArmor/HowToUse
   # https://help.ubuntu.com/12.04/serverguide/apparmor.html
   apt-get update
   apt-get install apparmor apparmor-profiles apparmor-utils apparmor-profiles-extra apparmor-easyprof -y
   sed -i -e 's/GRUB_CMDLINE_LINUX_DEFAULT="/&security=apparmor /' /etc/default/grub
   sed -e 's/GRUB_TIMEOUT=5/GRUB_TIMEOUT=1/' /etc/default/grub
   update-grub

- Setup auditd if you'd like. You can also send the logs to remote syslog-ng. Example audit.rules for EXEC logs:
    -a exit,always -F arch=b64 -F euid=0 -S execve
    -a exit,always -F arch=b32 -F euid=0 -S execve


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Kernel

- If you are compiling the kernel you may want ideas from:
    https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings

- Sysctl hardening options
    echo '''kernel.dmesg_restrict=1\nkernel.kptr_restrict=1\nkernel.kexec_load_disabled=1\nkernel.yama.ptrace_scope=1\nuser.max_user_namespaces=0''' >> /etc/sysctl.conf



=====
Firewall

- Disable IPv6
    echo 'blacklist ipv6' >> /etc/modprobe.d/blacklist
    echo net.ipv6.conf.all.disable_ipv6=1 > /etc/sysctl.d/disableipv6.conf
    echo "1" > /proc/sys/net/ipv6/conf/all/disable_ipv6
    echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6

- Configure firewall to DROP everything by default and allow only manadotory connections for root and the first user. For IPv4.
    #!/bin/bash
    IPT=/sbin/iptables
    $IPT -F
    $IPT -F -t nat
    $IPT -X
    $IPT -N Allower
    $IPT -A OUTPUT -j Allower
    $IPT -A Allower -m owner --uid-owner 0 -j ACCEPT
    $IPT -A Allower -m owner --uid-owner 1000 -j ACCEPT
    $IPT -A INPUT --in-interface lo -j ACCEPT
    $IPT -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
    $IPT -P OUTPUT DROP
    $IPT -P INPUT DROP
    $IPT -P FORWARD DROP

- Additional firewall hardening: match UID and only allow the users that really need network. The following example is DNS server ACCEPT.
    $IPT -A OUTPUT -m owner --uid-owner 112 -d 185.121.177.177 -p udp --dport 53 -j ACCEPT


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Remote management

- For enterprise, configure central management (eg. puppy, cf-engine or similar), that makes sure all users have the same config.

- SSH for remote management if needed, example settings:
    Port 1234
    ListenAddress 0.0.0.0
    PermitRootLogin without-password  # Use keys!
    PermitEmptyPasswords no
    PasswordAuthentication no  # Generate your SSH key with a password!
    AllowUsers user1 user2  # No other users will be allowed
    X11Forwarding no
    PermitTunnel no
    GatewayPorts no  # Note that it won't allow port forawrding!


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Browser basics

- Use the following extenstions for FireFox:
NoScript
HTTPS Everywhere
Privacy Badger


- Use the following extenstions for Chromium:
ScriptBlock
HTTPS Everywhere
Privacy Badger

You can also use privoxy in the place of Privacy Badger: https://www.privoxy.org/

Know that allowing javascript exposes you to hardcore tracking (eg. javascript audio API fingerprinting which is used by several big sites).



=========
Gentoo hardening points

Gentoo + musl + openrc or runit + luks (or zfs native enc) + zfs + apparmor or selinux
Plus CACert and repobuilds.