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Date: Fri, 27 Jan 2017 17:00:30 +0000
From: Daniel Elebash <danelebash@...mail.com>
To: "fulldisclosure@...lists.org" <fulldisclosure@...lists.org>
Subject: [FD] Digital Ocean ssh key authentication security risk -- password
 authentication is re-enabled

Regarding digitalocean.com cloud computing.


PasswordAuthentication is reset to yes in  /etc/ssh/sshd_config when using ssh key authentication given the following scenario:


When creating a new droplet from a snapshot where ssh key authentication "PasswordAuthentication" in /etc/ssh/sshd_config was previosly set to no, "PasswordAuthentication" is reset to yes.


I am not sure how common this scenario is but for me I often create a base snapshot that is pre-configured with firewall settings, sudo user, ssh key authentication, various apps, hardening etc. that I can then use when spinning up a new server so I don't have to start from scratch.  By doing this  I was unaware that PasswordAuthentication was automatically re-enabled and that these servers were no longer secure via ssh key authentication only, leaving them open to Brute Force attacks.


Steps to reproduce:

Tested using an Ubuntu 16.04 droplet image

1. Create a  new Ubuntu 16.04 droplet and secure it using ssh key authentication
2. Edit /etc/ssh/sshd_config and set PasswordAuthentication no
3. Reload ssh
4. Verify that you can log in using key authentication only, trying via password should be rejected.
5. Create a snapshot of this droplet
6. Create a new droplet from this snapshot
7. Open /etc/ssh/sshd_config and PasswordAuthentication will be reset to yes

You will now be able to log in via ssh using passwords instead of key authentication only.


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