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Linux Security - SSH Security Essentials

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[Music]

before we get started with today's video

i just want to take you through the

structure of

this particular series um so i've

actually partnered with linux to bring

you this series

this series will involve two parts so if

you head over to linux.com under

events you should find the hack exploit

linux live

linux server security series and you can

just click on more info here

so this series is going to be a 12-part

series on how to set up secure and audit

linux servers

uh and we'll begin on on the 1st of

october

and the first series will be available

on youtube and will include ssh security

essentials configuring sudo access

securing apache 2

securing engine x and the uncomplicated

firewall

the second part of the series will be

hosted on linux live

and it's absolutely free you don't have

to pay anything

and again you can access you can

actually register for that there this is

going to be an

advanced series that will build up or

build off

the first series and we'll cover things

like brute force protection

ip tables wordpress security and

security auditing on linux with

the linux tool um so to access that just

click on the registration link

on on the on24 platform and that will

take you here so that will give you an

idea of all the various web costs

and when they're going to be posted and

it'll give you a summary of what will be

covered exactly these are advanced uh

webcasts that will be about 40 minutes

and you can register for them absolutely

free of charge we've also

partnered with lino to give you guys a

free credit uh so again if you

are interested in using lynode for your

virtual private server or for your

hosting whether you're a developer or a

administrator uh you can get a hundred

dollars of 90 day credit

uh and this is for new accounts um so

that's fantastic

definitely do take advantage of this if

you're getting started with linux or

you're actually following uh you're

following along with this series

however make sure to actually redeem

this offer or this code

uh which is under promo.linu.com

and the code is hackersploit100 this

offer will only be limited till the

15th of december so definitely check

that out that being said let's get

started with today's video

hey guys hackersploit here back again

with another video welcome to the linux

security series

in this particular series we're going to

be taking a look at how to secure linux

systems and

more specifically linux servers now as

you've read from the title this video is

going to be about ssh security

so i'll be taking you through all these

essentials of securing ssh

we're not going to be taking a look at

brute force protection where i'm just

going to be showing you how to secure

ssh

and how to go about setting up ssh

securely

now in this particular video or in this

particular series we'll be following a

very important

a premise here or an example if you will

and the reason i'm doing this is to give

the videos a bit more context in in

regards to how you can apply these

techniques yourself when setting up a

server regardless of whether it's a

personal server

or whether you're setting up one for

your organization or for your company it

really doesn't matter

so the way i'm going to be doing this is

i'm going to be using

somewhat intricate but basic examples

again to give you

a better idea of of how you can apply

these techniques so

in this particular case uh we are going

to take a simple example of

the fact that i'm an administrator and

i've been

hired uh to again manage the company's

linux servers

on the cloud and also some various

on-premises servers that they have

and the development team that's

responsible for developing the web

applications that they have actually

told me the linux administrator to fire

up a few servers on the cloud

or virtual private servers uh for

wordpress

for a wordpress website so we have been

given that

that particular role or that particular

task and

our first order of business is to set up

remote authentication so that the

development

team can connect to the server and do

whatever they want and of course they're

going to be using ssh to do this so ssh

stands for secure shell it is a

remote authentication and remote control

remote

remote control protocol and it allows

you to connect to

linux servers remotely or even windows

servers

right so now that we have set up the

premise we can actually get started now

uh we have partnered with linux to

actually give you guys

some free credits or free access and you

can access this uh by going to

lynnote.com

and take a look at hackersploit so ford

slash hack exploit

and that will give you a free 20 credit

so you can actually

get started and follow along with this

if you want to uh and again you can

create as many linux as you want

and you get about 20 dollars which is

fantastic

excellent so we can now get started now

this is my dashboard

and you can see where we're going or

following along with the premise and

these are the servers that i'm currently

managing and i have the marketing server

and a project management server here

and now we've been told to create a new

linux server

with wordpress installed and we can go

about setting up

the security from the ground up so the

first thing we're going to do

is we're going to create a new linux so

i'll click on newly node

and again i can set up wordpress

manually or i can go into the

marketplace here which is great

a great feature offered by lenoid and i

have all of these

applications that again are

pre-configured to work

right out of the box so i can set up a

lamp server a lamp server

i can also set up a postgresql database

an open vpn

instance so that i can actually set up

my own openvpn server and then of course

we have the game servers which is

awesome

we have we also have the ability to set

up docker

which is fantastic you can actually just

get started immediately without setting

up or installing anything

in our case we're going for wordpress um

so i'm just going to go to the bottom

it's going to ask us for the wordpress

options

so again the development team is has

given us some some basic credentials and

of course

we're just going to uh we're going to

improvise a little bit so the user is

going to be user at uh test.com

and the admin username is going to be

admin and of course i don't recommend

doing that but that's

another topic for another video and then

of course for the password we're going

to give it a super secure password right

so i'll give it the best password i can

and we're going to disable this

gradually as we as we move along because

password-based authentication with ssh

not really recommended uh because you

know attackers can brute force the

server or brute force ssh

we then need to provide the database

password which again make sure that is

equally as

secure and landlord gives you a password

strength um

level right over here and the website

title we're just going to call this

development

development site this is where the you

know the development team is

going to just work on uh various

betas or new new web apps that they're

currently working on

and we don't have a domain yet so we're

not mapping it and the default uh

image is going to be debian which is

perfectly fine i then specify the region

and of course you can specify the region

that's most uh appropriate or

advantageous to you based on

uh what area or what part of the world

you're in

my case i'll just go for europe london

uk as that's the closest to me

and i can then specify my plan and of

course these are based on cpu uh

intensive or cpu dedicated cpus high

memory

based lino's and gpu based cleaners as

well which is great for

password cracking that's something i'll

probably want to cover in another video

um so i'll click on a one gigabyte uh

ram and one gigabyte oh sorry one cpu

a linode which is a nanode and that's

about five dollars a month

which is perfect so that'll be fine for

a wordpress server

and i'll just call this wordpress

development that's the name of the

server so wordpress development

and i'll enter a root password now you

can see a very interesting thing here

with most cloud providers and you know

linux

in particular is the ability to set up

ssh keys

which we'll be doing but there's a

there's there's a flaw here by default

and that is

the fact that you'll be logging in

directly to the server with the root

user account which is

our first order of business that we want

to change so we will stick to

you know authenticating with the

password first and i'll not add an ssh

key

yet because we're going to add it for a

different user

so i'll hit create and that's going to

create the linux instant in

instance for us so i'll just wait for

that to provision and to start and uh

yeah i'll just wait for that to complete

all right the node is created so we can

actually get started so i'm just going

to copy the ipv4 address here and we're

going to log in

using openssh or the openssh client now

as i said i'm currently

using linux ubuntu to be specific and of

course you can log in with various other

you know ssh clients like uh you have

putty on windows

and of course you have the open ssh

client installed by default on macos i i

believe

and on linux it's pretty much the same

so you want to make sure you have the

openssh client installed so sudo apt

install

um open ssh and we want to specify the

the open ssh client i believe there we

are and i'll just specify my password

here

and that's gonna tell me it's already

installed fantastic so to authenticate

via ssh we say ssh we specify the

username and

we'll paste in the ip of the server hit

enter that's going to ask us for the

root password um that we specified so

i'll just specify the root password here

and

we are logged in fantastic so now that

we have access to the server we can we

can get started with our first

our first priority which is to add

another user because

if i currently list out the users on the

system

you can see apart from the other service

based uh user accounts like mysql users

which is for the database and dub dub

dub data

you can see that we only have the root

user and we don't have any other user

accounts which is

is a problem because when we talk about

the root account

and uh in and permissions in regards to

the power of the root account

the root account is like the

administrator account which means you

can pretty much do

anything and if an attacker is able to

get access to the root account

remotely they can pretty they pretty

much take over the entire system they

can change passwords for the users they

can

they can you know delete databases dump

contents of databases so on and so forth

our first order of business is to

disable

the uh disable authentication remote

authentication to the server

with the root account and the way we do

that is first of all we segregate

duties on the server right so for the

development team we'll create

a user for them so that they don't have

to use the

the root user to log in so to do that we

use the user add command so user add

and i'll say m to create a home

directory and we specify the shell

which in this case is going to be bin

bash right and

and i'll create the username which is

just going to be dev and i hit enter so

we've added the user dev

and if i just print out the users now

you can see at the bottom we have the

user dev right over here and the home

directory

is listed as home dev so the next thing

we want to do is we want to assign a

password to the user dev so i say

password

and i specify the user dev so i say

password dev it's going to ask us to

specify a password for the user dev

which i will do and there we are so we

have now

added the user dev and we can try and

switch to that user by using this uh

super user or switch user there we are

so we say su

and we move on to the dev account and

you can see we can log in directly

and if i go to the home directory

you can see we are currently sorry pwd

we are currently in the home dev

directory here

we can also switch back to the root

account um like so and it's going to ask

us for the root account password

which works out fine so we our first

order of business as i mentioned

is to log in as to disable uh

authentication remote authentication

uh with the root account and to do this

we need to uh

we need to take a look at the ssh or the

open ssh daemon configuration file

because the thing you have to understand

about ssh it is a client server based

connection

which means there's the client and the

server this particular server is running

open ssh server so we need to

configure the openssh server settings so

we'll click we'll use

an editor i'm using vim you can use nano

so we want to go into the etsy directory

hc ssh and we're looking for sshd

now the reason we're looking for sshd

the d represents the daemon which

essentially means the service or the

server service and we're looking

and the sshd configuration file so i'm

just going to hit enter

and this is the configuration file over

here now there's tons of options that

you can change

and these options are not related uh you

know only to security

uh they also pertain or are also related

to things like networking we can change

the

default port that the service is

currently running on that's also very

helpful sometimes

and of course there's tons of other

options that we can change now the

option we're looking for

is an option called permit root login

now the interesting thing you'll see

about this file

is the syntax that is used now by

default within configuration files

a hash or a pound symbol represents a

comment which means that line

of code or that line is not active now

if you

see a line without a hash or a pound

that means that that

line is currently active in this case

all the lines with hashes or pound or

the pound symbols means they're left to

their default values

and open open ssh will will actually use

that by default

so any custom options will will not have

the pound or the

the hash symbol in this case permit root

to yes we want to disable that to know

now note this does not mean we cannot

use the root user that's something we'll

be disabling

in another video this just means we

cannot access

the server via ssh using the root user

after this we'll only be able to access

it using the dev user

so we'll say permit root login to no we

want to say no to that

and then to save this file i'll just use

wnq

to write and quit and we can now quit

there we are fantastic

so now i can just exit from the server

so i'll just exit from both users there

we are

and if i try and access the server using

the root user again

you'll see something interesting happen

here and of course i think i'll be able

to authenticate because i haven't

restarted the service

so i'll just do that right now so sudo

system control uh restart

ssh and i'll that will restart the

service and if i try and log in again

now it's gonna ask me for my password

and if i enter the password

it's gonna tell me i'm unable to

authenticate so we'll just wait there we

are permission denied try again

and that doesn't necessarily mean that

my uh my password is incorrect or i've

done anything wrong

it just means that i cannot log in to

the root user

uh with a password i cannot authenticate

with the root user of issh and of course

you can see that that

that option is explicitly defined within

the configuration file because

it does it does offer a a reprieve in

terms of security because

a lot of attackers will target the root

account because it off

it offers the lowest hanging fruit um

right so that means we can only access

the server via the dev user

all right so i'll open up the dev user

right over here fantastic so i'll

specify the

um i'll specify the password for the dev

user and i have access and of course

i can switch back into the root user if

i want to by saying su

root and there we are

fantastic so again i can i can always

access the root user but that's

something we'll also want to be

disabling because

uh the dev user if compromised can still

in some way

access the root account if they have the

password in most cases that's not going

to be the case

but now we have to secure the dev user

and the way we're going to be doing that

by using ssh keys now as i said

we can set up ssh keys by default with

the cloud provider likely known however

that does it for the root user

we want to do this for the dev user so

we are slowly segregating

and uh lowering our our security risk

because we are setting up users based on

privilege

and number two we are also increasing

the

the amount of uh authentication security

in place

so to get started what we want to do is

i'll open up a new tab on in my terminal

here

and we want to generate our ssh key now

or you can generate your ssh key

very very simply on linux by specifying

ssh

keygen so if i say ssh keygen

like so you can see it gives me the

ability to generate a key so

sh key then i can then specify t rsa

that is the pro

the algorithm that is being used and

on windows you can do it you can also

generate your ssh keys

using using putty if you want and i'm

going to

enter and it's going to tell us it's

generating the public

private rsa key pair and it's going to

save it into the default home directory

under ssh here

in most cases you just want to leave

that as it is so i'm just going to enter

and it's going to tell me it already

exists and i'm going to overwrite this

for a very important reason i'll hit

enter

now ssh keys also allow you to specify a

passphrase this is like two-factor

authentication because

in addition to your ssh keys uh you can

also

uh secure them with a password so if

someone gets a hold of your ssh key

they'll not be able to authenticate

without that particular passphrase in my

case i'm not going to enter a passphrase

so i'm just going to hit enter right and

your your uh your keys are going to be

stored

within your home uh your home directory

under ssh

and the file is going to be called id

rsa that's your private key

and you have idrsa.pub which means

public in that we can

list out the contents of my ssh

directory here

so ssh and um if i list it you can see

we have the private key this is what we

want to keep securely

and we have the public key now of course

when we talk about

the the public key as i said we need to

copy this onto the server

so how do we do this well we can we can

copy it manually however much easier way

of doing it

is through a utility called ssh copy id

so we say ssh copy

id and then we specify the user that we

we want to authenticate as so dev

at and then i paste in the ip of the

server and i hit enter and that's going

to copy our public key to the server

so we're just going to wait for that to

prompt us to authenticate with the

password

so it's going to say enter our password

for the dev user so there we are

it's going to now tell us the number of

keys added is two

right so we've added two keys here and

um there we are so we've added our key

and that means we can now authenticate

to the um

we can all authenticate to the server

without entering a password for the dev

user that's only for

us however a password-based

authentication is still available so

i'll just explain this to you shortly so

if i try and log in to the ssh

to the server of issh using the dev user

you'll see that i'll be able to log in

without entering a password so i'll hit

enter

it's going to use my private key and

again we'll just

sorry that is an incorrect ip let me

just paste in the correct one

which is this one right over here if i

just paste that in here

and you can see i'll now be able to

authenticate without entering any

password there we are

i'm now logged in as dev at the lynnode

instance right over here

so i didn't have to enter any password

although password-based authentication

is still set up

now if i try and authenticate using

another system like my windows system

with putty

and i'll just open up lynode and copy

the ip there and i try and log in

let's open up putty again uh like so

you can see that it still is going to

ask me for my

password so i'll say you log in as dev

it's going to ask me for my password

and i can still log in regardless of

whether i've set up an ssh key we need

to remedy this

the way we remedy this is by disabling

uh password logins or disabling uh

password-based authentication so what

i'm going to do is i'm just going to

minimize that and i'll switch into the

root user

so i'll say su root and it's going to

ask me for my root password

there we are and we'll go back into the

sshd

configuration file so we're looking into

the

hc ssh and sshd

configuration file and we want to go

we want to go all the way to the bottom

here right over

it should be over here uh under

authentication

we have changed permit root login to no

and we just want to go slightly to the

bottom here on

under disable tunneled clear text

password so

to disable tunnel clear text passwords

change to no here so

for password authentication we want to

disable this so we

we again will just get rid of the the

pound or the hash symbol

and we're going to set the option to no

right so we'll set that to no

now what this means is that under no

circumstance are we going to be able to

access this server

using passwords the only way we're going

to be accessing this server

is through our ssh keys so that's

something you want to take into

consideration before you activate this

particular option or this particular

setting

make sure you have the ssh key available

because there'll be no way you'll be

able to get access to this via ssh then

so i'll write in i'll write the changes

and save it and again in this case i'll

just restart ssh so

system control restart ssh

sorry ssh like so and if i now exit or i

log out

again on this system i'll be able to log

in without the password because i have

the ssh key

and i can then share this ssh key with

the development team and they'll be able

to log in using the ssh key

so if i hit enter you'll be able to see

there we are i have access i still have

access here

however if i go on over to my windows

system and i try and

uh log in using putty so what i'll do is

i'll just

open up a new session here i'll close

that one

and i'll just copy the ip one more time

here just to make sure i have the right

one

and uh i'll open up putty

let me just load my profile hit open

you can now see if i try and say login

as dev it's going to give me an error

telling me no supported authentication

methods available

server sent public key so again that

means that

now on this server there's no way we are

authenticating with

with any password of any kind regardless

of the user

so again we've disabled uh the root user

logins which is very important number

two

we've set up and secured the other user

account which is the dev user the only

way

anyone is logging onto it now is through

the ssh key

and of course as i said the ssh key is

going to be under your home directory in

ssh

uh and it's um it's the the file that is

in uh

that we're referring to is the id rsa

key right over here so this is the file

you want to share with the development

team

and again they can then use it to log in

however as i mentioned it's very

important

to take into consideration the fact that

you want to keep the private key

as personal and as private as possible

that's the reason it has the name

private uh now of course in the next

videos we'll be talking about uh giving

the dev uh the dev user account the

appropriate permissions to run

administrative tasks

like installing software updating

software and we'll also then go a step

further

by disabling the root account

permanently so that you cannot even

switch to it in the event an attacker is

able to compromise the system

through one of the lower privileged

accounts like the dev user they'll not

be able to get

access to the root account that being

said that's going to be it for this

video

let me know what you thought in the

comments if you have any questions or

suggestions and i'll be seeing you

in the next video i just want to take a

moment to thank all our patreons at

patreon.com forward slash hackersploit

for all

the support your support and help is

truly appreciated you keep us making uh

newer and fresher

and better content so i just want to say

thank you to all the patreons

so thank you murph the surf daniel bork

jonathan kyle

adam mack jamal guillory defean barry

jeremy nikolai

marie harrah max ciao dustin empress

michael hubbard and jerry speds

you

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