Table of Contents

Originally written April 2016, updated March 2022

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Never Forget

Never Forget DSA-3733, aka Validating signatures > MitM > RCE

The Debian developer community refused to implement transport cryptography for updates because “signing packages is secure enough”. Fuck that incompetence. This post is about "the how". If you want to read about "the why", please read my earlier post: https://yawnbox.com/blog/privacy-proposal-for-debian/

This is a quick guide on how to significantly improves the privacy and security of your Ubuntu server. It requires the installation of apt-transport-tor, an application that will allow apt transfers to occur over Tor. There is also an application called apt-transport-https that is already installed in Ubuntu 20.04 that we’ll leverage first.

The Wikimedia Ubuntu repo has a good TLS configuration, IPv6 and IPv4 support, and they don't block Tor: mirrors.wikimedia.org

Qualys SSL Labs grade: https://www.ssllabs.com/ssltest/analyze.html?d=mirrors.wikimedia.org&latest

If you only want increased security, this is what your /etc/apt/sources.list should look like:

deb https://mirrors.wikimedia.org/ubuntu/ focal main restricted universe multiverse
deb https://mirrors.wikimedia.org/ubuntu/ focal-updates main restricted universe multiverse
deb https://mirrors.wikimedia.org/ubuntu/ focal-backports main restricted universe multiverse
deb https://mirrors.wikimedia.org/ubuntu/ focal-security main restricted universe multiverse

If you want security and privacy, use tor.

Ubuntu Server 20.04 Focal apt privacy upgrade script

#!/bin/bash

mv /etc/apt/sources.list /etc/apt.sources.backup1

touch /etc/apt/sources.list

echo 'deb https://mirrors.wikimedia.org/ubuntu/ focal main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb https://mirrors.wikimedia.org/ubuntu/ focal-updates main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb https://mirrors.wikimedia.org/ubuntu/ focal-backports main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb https://mirrors.wikimedia.org/ubuntu/ focal-security main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb [arch=amd64] https://deb.torproject.org/torproject.org focal main' >> /etc/apt/sources.list

wget -qO- https://deb.torproject.org/torproject.org/A3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89.asc | gpg --import

gpg --export A3C4F0F979CAA22CDBA8F512EE8CBC9E886DDD89 | apt-key add -

apt update

apt install tor deb.torproject.org-keyring apt-transport-tor -y

mv /etc/apt/sources.list /etc/apt.sources.backup2

touch /etc/apt/sources.list

echo 'deb tor+https://mirrors.wikimedia.org/ubuntu/ focal main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb tor+https://mirrors.wikimedia.org/ubuntu/ focal-updates main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb tor+https://mirrors.wikimedia.org/ubuntu/ focal-backports main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb tor+https://mirrors.wikimedia.org/ubuntu/ focal-security main restricted universe multiverse' >> /etc/apt/sources.list
echo 'deb [arch=amd64] tor+https://deb.torproject.org/torproject.org focal main' >> /etc/apt/sources.list

apt update && apt dist-upgrade -V

Or, if you trust me, run this script:

curl -s https://yawnbox.com/scripts/focal_apt_upgrade.sh | sudo sh

All your future apt update and dist-upgrade commands will now be performed via high-grade TLS over Tor.

March 2022 update

DNS needs love too. If you are reading this and know of a way to push DoT or DoH traffic out Tor (like with a SOCKS5 proxy pointing to 127.0.0.1:9050 or something), please send me a message!

Edit Netplan:

sudo vim /etc/netplan/01-netcfg.yaml 

Add Quad9 nameservers:

      nameservers:
              addresses:
                      - 9.9.9.9
                      - 149.112.112.112
                      - 2620:fe::fe
                      - 2620:fe::9

Apply netplan changes:

sudo netplan apply

Edit resolved.conf by enabling DNSOverTLS:

sudo sed -i 's/#DNSOverTLS=no/DNSOverTLS=yes/g' /etc/systemd/resolved.conf

sudo cat /etc/systemd/resolved.conf

Output should look like:

[Resolve]
#DNS=
#FallbackDNS=
#Domains=
#LLMNR=no
#MulticastDNS=no
#DNSSEC=no
DNSOverTLS=yes
#Cache=no-negative
#DNSStubListener=yes
#ReadEtcHosts=yes

Restart systemd-resolved:

sudo systemctl restart systemd-resolved.service

You can validate this by using ufw. If, like me, you are denying all outbound (ufw default deny outgoing), all you have to do is delete the allow out 53/udp rule, and add an allow out 853/tcp rule. Otherwise, add a deny out 53/udp rule and test.

sudo ufw delete 53/udp
sudo ufw allow out 853/tcp
sudo ufw reload

or

sudo ufw deny out 53/udp
sudo ufw allow out 853/tcp
sudo ufw reload

Then simply try an outbound web request, like with sudo apt update! If it works, then your DNS queries are TLS encrypted to Quad9!

yawnbox