A hacker’s perspective: social media account takeover prevention guide

“If you watched the SEC Twitter account hack that moved markets yesterday and wondered how to prevent account takeover for your personal, business, or high profile social media account, here’s an Account Takeover Prevention Guide for you and/or your organization.” @racheltobac neatly summarises the steps you should take to prevent the hijacking of your online accounts.


Install and configure SSH on Debian or Ubuntu

SSH is a protocol that enables secure connections over unsecured networks. It supports the use of asymmetric encryption for user authentication. Private keys are kept locally, while public keys are stored on the remote machine.

The following configuration disables root logins on the remote machine. Only users belonging to the group ssh-users may establish a connection. Access to the remote machine is tied to the local user’s private key.

In this example, the name of the remote machine is debian-server, which has the address on the network. sid is a user on debian-server, whereas bookworm is a user on the local machine. Choose an encryption passphrase to secure the private key that you will generate in Step 5.

On the remote machine

Step 1

Install the secure shell server with the following command:

$ sudo apt install --yes openssh-server

Step 2

If you are using ufw as a host-based firewall

Configure ufw to allow connections to the secure shell server.

$ sudo ufw limit ssh

If you are using firewalld as a host-based firewall

Configure firewalld to allow connections to the secure shell server.

$ sudo -- bash -c 'firewall-cmd --zone=public --add-service=ssh --permanent && firewall-cmd --reload && firewall-cmd --info-zone=public'

Step 3

Restrict access to the remote machine to members of a specific group. Start by creating the group ssh-users.

$ sudo addgroup --system ssh-users

Add the user sid to the group ssh-users.

$ sudo adduser sid ssh-users

On the local machine

Step 4

Install the secure shell client with the following command.

$ sudo apt install openssh-client

Step 5

Generate a new key pair for the local user bookworm:

$ ssh-keygen -t ed25519 -o -a 100

Save the key pair to the directory /home/bookworm/.ssh/. Choose a name that facilitates easy identification.

Enter file in which to save the key (/home/bookworm/.ssh/id_ed25519): ~/.ssh/id_ed25519-debian-server

The use of an appropriate passphrase to secure the private key is mandatory.

Step 6

Create the file ~/.ssh/config to configure the secure shell client.

$ nano ~/.ssh/config

Add the follwing minimal entry for the host debian-server.

Host debian-server
   IdentitiesOnly yes

Step 7

Deploy the public key with the following command.

$ ssh-copy-id -i ~/.ssh/id_ed25519-debian-server.pub sid@debian-server

Step 8

Log into the remote machine.

$ ssh -i ~/.ssh/id_ed25519-debian-server sid@debian-server

When prompted to confirm the authenticity of the host debian-server, type yes and press [Enter].

The authenticity of host 'debian-server (' can't be established.
ED25519 key fingerprint is SHA256:C9RxLLVbvFwVJc0L4JHzcuHQSaPHJZe/GrRDvqy6rAG.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])? 

In the next step, enter the passphrase for your private key.

Enter passphrase for key '/home/bookworm/.ssh/id_ed25519-debian-server':

Step 9

On the remote machine, download a file to harden the ssh server. You are encouraged to inspect its contents.

$ sudo -- bash -c 'wget -P /etc/ssh/sshd_config.d/ --show-progress https://edafe.de/debian/sshd_config.conf'

Activate the modifications on the remote machine.

$ sudo systemctl restart ssh.service

Step 9

On the local machine, open a new terminal window and run the following command.

$ ssh -i ~/.ssh/id_ed25519-debian-server sid@debian-server

In the next step, enter the passphrase for your private key.

Enter passphrase for key '/home/bookworm/.ssh/id_ed25519-debian-server':

Display the active configuration for the remote ssh server and verify its settings, paying particular attention to options for maxauthtries, permitrootlogin and passwordauthentication.

$ sudo sshd -T

All done!

For more in-depth information, please see stribika’s post-Snowden advice on hardening OpenSSH server installations.

The book SSH The Secure Shell by Daniel Barrett, Richard Silverman and Robert Byrnes is still useful today and has information on other clever stuff you can do with SSH.

The process of security

“Security is a process, not a product. Products provide some protection, but the only way to effectively do business in an insecure world is to put processes in place that recognize the inherent insecurity in the products.” Bruce Schneier acknowledges that in information technology perfect security probably doesn’t exist.


Trust the process, Tina!

Scaring people into supporting backdoors

“Beware the Four Horsemen of the Information Apocalypse: terrorists, drug dealers, kidnappers, and child pornographers. Seems like you can scare any public into allowing the government to do anything with those four.” Bruce Schneier re-emphasises the need for strong encryption as a matter of personal and national security.


Die AAA-Bürger

“So wie Alibaba und Amazon wissen, wofür sich ihre Nutzer interessieren und was sie als Nächstes kaufen könnten, will der chinesische Staat aus den Datenspuren seiner Bürger ableiten, wie sie sich in der Vergangenheit verhalten haben und in der Zukunft verhalten könnten und sie nach einem Punktesystem entsprechend bewerten. Wer zum Beispiel über das Internet gesunde Babynahrung bestellt, soll Pluspunkte erhalten. Wer sich hingegen Pornos ansieht oder zu viel Zeit mit Computerspielen verbringt, muss mit Abzügen rechnen.” Da trifft es sich gut, daß Felix Lee nichts zu verbergen hat und ein solcher Umgang mit Nutzerdaten überhaupt nur in China in Erwägung gezogen wird…


With thanks to Michael August.

Wie, Du bist nicht bei Whatsapp?

“Wer Whatsapp liebt, sollte besser nicht weiterlesen, oder vielleicht gerade dann, denn Liebe macht ja bekanntlich oft blind.” Boris Pohler, selbst Lehrer und Vater von zwei Kindern, bennent den Preis für die Verwendung des weit verbreiteten Dienstes und erklärt, warum jeder Nutzer gegen deutsches Recht verstößt.


Terrorists don’t scare city cyclists. We already have to deal with cars.

“If there’s one group of road users virtually immune to being cowed by a lowly act of terrorism involving a motor vehicle, it’s cyclists. We’re reminded every day—through rolled-down car windows, on too-narrow roads, via social media—that we “share” the roads with people who actively hate us and that our interests (including safety) come behind theirs. Every one of us knows what it’s like to stare death in the grille. Daily riders have all had drivers aim their cars at us as if they were about to plow us down, whether because of run-of-the-mill inattention or out-and-out road rage. This reality is priced into our decision to ride.” Eben Weiss alias Bike Snob NYC offers the urban cyclist’s perspective on the latest terrorist threat.


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