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Bandit13->14

Level Goal

Commands useful to solve the level

Helpful Reading Material

Where to start?

First, we need to know what is in our directory. Here is the output from the ls command : 

bandit13@bandit:~$ ls
sshkey.private
bandit13@bandit:~$
from now on we can already use that ssh key to connect to bandit14 user. However, we'll first retrieve the ssh key on our machine so that we can log into the user bandit14 without the need to be logged in as the user bandit13.

Part 1 : Retrieval of the ssh key

To retrieve the ssh key using the ssh protocol, we're going to need the command that stands for secure copy, the scp command.

Hint

Reading the scp man page, can you figure out a way to retrieve the ssh key from the bandit13 user on the overthewire server?

Solution

We'll have to run the command while not connected to the remote server, as the scp protocol will connect to the remote server and retrieve the file for us.
From the scp man page, we know the following : "The source and target may be specified as a local pathname, a remote host with optional path in the form [user@]host:[path], or a URI in the form scp://[user@]host[:port][/path].
Local file names can be made explicit using absolute or relative pathnames to avoid scp treating file names containing ‘:’ as host specifiers.". One precision to add is that the path argument is starting from the user's home directory.

Thus we can deduce the structure of the call we have to make : - For the source, we will specify the URI as follows : scp://bandit13@bandit.labs.overthewire.org:2220/sshkey.private - For the target, we will specify the local pathname we want to store the file in, let's say : ./bandit14_sshkey

Thus, the command we're looking for is : 

scp scp://bandit13@bandit.labs.overthewire.org:2220/home/bandit13/sshkey.private ./bandit14_sshkey

Part 2 : Setting the right file permissions

Now that we have a private ssh key, we need to use it to connect other ssh. To do so, as it is a private ssh key, it must meet some requirements on the file permissions. Our goal is to set the proper file permissions for us to be allowed to connect to the user bandit14.

Hint

By looking into the FILES section of the ssh man page and the chmod gnu documentation page, can you figure out the proper file permissions for the private key and set them accordingly?

Solution

In the portion describing the file ~/.ssh/id_rsa, we can read that this file should be readable by the user and should not be accessible by others.
Running the stat utility on the file gives us the file permissions of our ssh private key. Here is the output from this command :

  File: bandit14_sshkey
  Size: 1679        Blocks: 8          IO Block: 4096   regular file
Device: 804h/2052d  Inode: 8913955     Links: 1
Access: (0640/-rw-r-----)  Uid: ( 1001/ Charystag)   Gid: ( 1001/ Charystag)
Access: 2024-06-03 21:05:42.285372019 +0200
Modify: 2024-06-03 21:05:11.765802230 +0200
Change: 2024-06-03 21:05:11.765802230 +0200
 Birth: 2024-06-03 21:05:11.733802682 +0200

We can now see, (helping ourselves from the documentation about file permissions) that this file is readable and writable by the user and readable by the other members of the user's group. As we don't need to write data to the private key file, we can restrict the permissions to the minimum, we'll only allow the current user (us) to write to the file.
The following call to the chmod utility will allow us to achieve our goal : chmod 400 bandit14_sshkey.

Part 3 : Connecting using the ssh key

Now that the proper file permissions are set, the last thing we need to do is to connect to the user bandit14 using our private ssh key.

Hint

Going back into the ssh(1) man page, can you figure out an option that would allow us to use the ssh key we just got to connect to the user bandit14 ?

Solution

The option we're looking for is the option -i which allows us to use our identity_file to connect without the need for a password. This is our full command :

ssh -p 2220 -l bandit14 -i bandit14_sshkey bandit.labs.overthewire.org
Full Solution
  1. scp scp://bandit13@bandit.labs.overthewire.org:2220/home/bandit13/sshkey.private ./bandit14_sshkey to retrieve the private ssh key from the bandit13 user
  2. chmod 400 bandit14_sshkey to set the right file permissions and allow us to connect over ssh
  3. ssh -i bandit14_sshkey ssh://bandit14@bandit.labs.overthewire.org:2220 to finally connect to user bandit14

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